Welcome ! 👋

Thanks for checking out this js-challenger solutions repo.

What is JSchallenger ? 🙂

JSchallenger is a cool and great site to practice most of the JS fundamentals and JS dom. It's a very helpful Javascript resource for beginners. JSchallenger created by Erik Kückelheim. thanks Erik.

Why this repo ? 😶

In this repo, you can find available solutions for a challenge.

Table of solutions

Javascript Basics
variables
booleans
1. Assign boolean to a variable
2. Convert Number to Boolean
operators
strings
conditionals
1. if statement - satisfy condition
2. if statement - add missing condition
functions I
arrays

loops
asynchronous javascript
1. Execute the code synchronously
2. Execute the code asynchronously
Javascript Practice
Javascript fundamentals
Javascript arrays
Javascript objects
Javascript dates
Javascript Sets
Javascript DOM
DOM selector methods
Events and user interactions
DOM manipulation
1. Remove element from the DOM
2. Change id of HTML element
DOM fundamentals
Recursive functions
1. Stop and restart the moving button

Javascript Basics :

variables

Reassign a value to a variable

scenario :

Assign a new value to the variable num. The code will not work the way it is. Find the 
mistake and fix it. Execute the corrected code.

code scenario :

let num = 1;
let num = 2;
console.log(num);

Solution 1

js :

let num = 1;
num = 2;
console.log(num);

Back to table ⬆

Assign a value to a variable

scenario :

Here, we declare the variable num. But, it has no value yet. Assign a value to it and run 
the code.

code scenario :

let num;
console.log(num);

Solution 1

js :

let num;
num = 2;
console.log(num);

Back to table ⬆

Assign the value of another variable

scenario :

Here, we have two variables numOne and numTwo. numOne already has a value. Assign 
numTwo the value of numOne and run the code.

code scenario :

let numOne = 5;
let numTwo;
console.log(numTwo);

Solution 1

js :

let numOne = 5;
let numTwo = numOne;
console.log(numTwo);

Back to table ⬆

Create the missing variable

scenario :

Below, we attempt to assign the value of a variable named numOne to the variable 
numTwo. But, that variable has not been declared yet. Declare a variable named numOne 
and run the code.

code scenario :

let numTwo = numOne;
console.log(numTwo);

Solution 1

js :

let numOne = 5;
let numTwo = numOne;
console.log(numTwo);

Back to table ⬆

Accessing a variable 1

scenario :

In this simple exercise we declare a variable called num and assign it a value of 5. Then 
we try to log the value of the variable using the console.log() method.
But, the console.log() method contains a small mistake. If you try the run the code, you 
will see an error message.
Fix the mistake and run the code again.

code scenario :

const num = 5;
console.log(Num);

Solution 1

js :

const num = 5;
console.log(num);

Back to table ⬆

Accessing a variable 2

scenario :

This exercise is very similar to the previous one. We declare a variable called num, assign 
it a value of 5, and try to log it. But again, we introduced a small mistake.
Fix the code and run it.

code scenario :

console.log(num);
const num = 5;

Solution 1

js :

const num = 5;
console.log(num);

Back to table ⬆

Declare a variable and assign a number

scenario :

In this exercise we practice how to declare a new variable and how to assign it a number. 
The console.log() statement below attempts to log a variable named num.
Declare a variable with this name and assign it a number of your choice. Run the code to 
see if the number is being logged.

code scenario :

console.log('The value of num is: ' + num);

Solution 1

js :

const num = 5;
console.log('The value of num is: ' + num);

Back to table ⬆

Reassign a value to a variable 2

scenario :

Here again, we want to assign a new value to a variable that we previously declared. Again, the code will not work the way it is. Find the mistake and fix it. Execute the corrected code.

code scenario :

const text = 'hello';
text = 'hello world';
console.log(text);

Solution 1

js :

let text = 'hello';
text = 'hello world';
console.log(text);

Back to table ⬆

booleans

Assign boolean to a variable

scenario :

Here, we declare the variable isTrue. But, it has no value yet. Assign a boolean value to it and run the code.

code scenario :

let isTrue;

console.log(isTrue);

Solution 1

js :

let isTrue;
isTrue = true;
console.log(isTrue);

Back to table ⬆

Convert Number to Boolean

scenario :

Here, we declare the variable num and assign it the value 5. We also declare the variable bool which we assign the boolean 
representation of num.
Extend the code such that the console.log() statement logs false.

code scenario :

let num = 5;

const bool = Boolean(bool);
console.log(bool);

Solution 1

js :

let num = 5;
num = 0;
const bool = Boolean(bool);
console.log(bool);

Back to table ⬆

operators

Comparison operators - Equal

scenario :

In the console.log() statement below we use the Equal operator to check whether numOne and numTwo have the same value. Change the code so that the console.log() statement logs true.

code scenario :

const numOne = 5;
const numTwo = 6;
console.log(numOne == numTwo);

Solution 1

js :

const numOne = 5;
const numTwo = 5;
console.log(numOne == numTwo);

Back to table ⬆

Comparison operators - Not Equal

scenario :

In the console.log() statement below we use the Not Equal operator to check whether numOne and numTwo have different values. Change the code so that the console.log() statement logs true.

code scenario :

const numOne = 5;
const numTwo = 5;
console.log(numOne != numTwo);

Solution 1

js :

const numOne = 5;
const numTwo = 6;
console.log(numOne != numTwo);

Back to table ⬆

Comparison operators - Greater than

scenario :

In the console.log() statement below we use the Greater Than operator to check whether the value of numOne is greater than the value of numTwo. Change the code so that the console.log() statement logs true.

code scenario :

const numOne = 5;
const numTwo = 6;
console.log(numOne > numTwo);

Solution 1

js :

const numOne = 6;
const numTwo = 5;
console.log(numOne > numTwo);

Back to table ⬆

Comparison operators - Less than

scenario :

In the console.log() statement below we use the Less Than operator to check whether the value of numOne is less than the value of numTwo. Change the code so that the console.log() statement logs true.

code scenario :

const numOne = 2;
const numTwo = 1;
console.log(numOne < numTwo);

Solution 1

js :

const numOne = 1;
const numTwo = 2;
console.log(numOne < numTwo);

Back to table ⬆

Comparison operators - Greater than or equal

scenario :

In the console.log() statement below we use the Greater Than Or Equal operator to check whether the value of numOne is greater than or equal the value of numTwo. It also checks whether the value of numTwo is greater than or equal the value of numThree. Change the code so that both expressions in the console.log() statement logs true.

code scenario :

const numOne = 3;
const numTwo = 4;
const numThree = 2;
console.log(numOne >= numTwo, numTwo >= numThree);

Solution 1

js :

const numOne = 3;
const numTwo = 2;
const numThree = 2;
console.log(numOne >= numTwo, numTwo >= numThree);

Back to table ⬆

Comparison operators - Less than or equal

scenario :

In the console.log() statement below we use the Less Than Or Equal operator to check whether the value of numOne is less than or equal the value of numTwo. It also checks whether the value of numTwo is less than or equal the value of numThree. Change the code so that both expressions in the console.log() statement logs true.

code scenario :

const numOne = 1;
const numTwo = 4;
const numThree = 2;
console.log(numOne <= numTwo, numTwo <= numThree);

Solution 1

js :

const numOne = 1;
const numTwo = 1;
const numThree = 2;
console.log(numOne <= numTwo, numTwo <= numThree);

Back to table ⬆

strings

Create a Javascript string

scenario :

In this exercise the existing console.log() statement logs the value of the variable text. The variable text has already been declared with an empty string – as indicated by the two single quotes.
Fill in the string with some characters and run the code to see if the string is being logged.

code scenario :

const text = '';
console.log('The value of text is: ' + text);

Solution 1

js :

const text = 'hello world';
console.log('The value of text is: ' + text);

Back to table ⬆

Different ways to create Javascript strings

scenario :

Here, we have declared 3 variables textOne, textTwo, and textThree. An empty string is assigned to all of them.
Do you see how in each case different symbols are used to create the string? All three of them are valid methods to create a JavaScript string.
Fill in all 3 strings with some characters and run the code to see if the values get logged.In this exercise the existing console.log() statement logs the value of the variable text. The variable text has already been declared with an empty string – as indicated by the two single quotes.
Fill in the string with some characters and run the code to see if the string is being logged.

code scenario :

const textOne = '';
const textTwo = "";
const textThree = ``;
console.log(textOne, textTwo, textThree);

Solution 1

js :

const textOne = 'Hello, ';
const textTwo = "it's ";
const textThree = `me`;
console.log(textOne, textTwo, textThree);

Back to table ⬆

Connect Javascript strings 1

scenario :

After we have learnt how to create JavaScript strings, we will now connect 2 strings together. In the code below we use the Addition (+) operator to concatenate textOne and textTwo. The console.log() statement logs the resulting string. Currently, the result would be HelloWorld.
Change the code below so that the value of res is Hello World

code scenario :

const textOne = 'Hello';
const textTwo = 'World';
const combined = textOne + textTwo;
console.log(combined);

Solution 1

js :

const textOne = 'Hello';
const textTwo = 'World';
const combined = textOne + ' ' + textTwo;
console.log(combined);

Back to table ⬆

conditionals

if statement - satisfy condition

scenario :

In this exercise we will work with our first if-statement. In the code below we declare a variable num with a value 0. Then, we have an if-statement. The if-statement consists of a condition – the part inside the parentheses – and some code inside a pair of curly braces. The code will assign the variable num a new value 1. But it will only run if the condition is met.
Adjust the condition such that the code inside the curly braces will execute and the console.log() statement logs true.

code scenario :

let num = 0;
if (1 > 2) {
   num = 1;
}
console.log(num === 1);

Solution 1

js :

let num = 0;
if (1 < 2) {
   num = 1;
}
console.log(num === 1);

Back to table ⬆

if statement - add missing condition

scenario :

Time to practice what we've learnt so far. In the code below, the if...statement will assign a new value to the variable text. But only if its condition is met. Currently, the condition is missing.
Add any condition that will be satisfied such that the console.log() statement logs true.

code scenario :

let text = 'hello';
if () {
   text = text + ' world';
}
console.log(text === 'hello world');

Solution 1

js :

let text = 'hello';
if (text === 'hello') {
   text = text + ' world';
}
console.log(text === 'hello world');

Back to table ⬆

functions I

Function declaration

scenario :

In this exercise we will work with our first JavaScript function. In the code below we create a function named func. This way of creating functions is called function declaration: the keyword function followed by the name of the function and a pair of parentheses. Then follows some JavaScript code wrapped by curly braces.
Notice that we use the return keyword to make the function return a value, in this case a string.
When we create a function in JavaScript, the statement inside the curly braces is exectued only when the function is called. You can call a function by using its name and a pair of parentheses func().
Below, we call our function and assign its return value to the variable result. Then, we log the result. To solve this exercise simply have the console.log() statement log the words hello world.

code scenario :

function func() {
    return 'hello';
};
const result = func();
console.log(result);

Solution 1

js :

function func() {
    return 'hello world';
};
const result = func();
console.log(result);

Back to table ⬆

Function expression

scenario :

In this exercise, we use a slightly different way to create a function – a function expression. Here, we create a function and assign it to the variable func. Notice that we omit the name of the function after the function keyword. We call this function the same way as in the previous exercise. But, instead of using the name of the function itself, we call it using the name of the variable to which the function was assigned.
In the code below, we introduced a small mistake when calling the function. Find the mistake and run the code to see if the words hello world are correctly logged.

code scenario :

const func = function() {
    return 'hello world';
};
const result = func;
console.log(result);

Solution 1

js :

const func = function() {
    return 'hello world';
};
const result = func();
console.log(result);

Back to table ⬆

Correctly return value from function 1

scenario :

In this exercise, we create a function func. Then, we call func and assign its return value to the variable result.
When you run the code like this, you see that the value undefined is logged. This is the current return value of func because we do not explicitly define a return value ourselfs.
Let func return the value of the variable text.

code scenario :

const func = function() {
    let text = 'hello';
    text = text + ' world';
};
const result = func();
console.log(result);

Solution 1

js :

const func = function() {
    let text = 'hello';
    text = text + ' world';
    return text;
};
const result = func();
console.log(result);

Back to table ⬆

Correctly return value from function 2

scenario :

In this exercise, func declares a variable text with the value hello. Then it returns the value of text. After that, it assigns a new value hello world to the variable text and returns the new value.
But, when you run the code, you see that only the initial value of text (hello) is logged. This is because once a function call reaches a return statement, further function execution is stopped. All code after the return statement is ignored.
Adjust the code so that the final value of text is logged.

code scenario :

const func = function () {
    let text = 'hello';
    return text;
    text = text + ' world';
    return text;
};
const result = func();
console.log(result);

Solution 1

js :

const func = function () {
    let text = 'hello';
    text = text + ' world';
    return text;
};
const result = func();
console.log(result);

Back to table ⬆

arrays
loops

asynchronous javascript

Execute the code synchronously

scenario :

Adjust the code snippet so that the console.log statement logs the value 2.

code scenario :

let i = 0;
function func() {
 i = 2;
}
setTimeout(func, 100)
// expected output = 2
console.log(i);

Solution 1

js :

let i = 0;
function func() {
 i = 2;
}
func();
// expected output = 2
console.log(i);

Back to table ⬆

Execute the code asynchronously

scenario :

Adjust the code snippet so that the value 0 is logged first and then the value 1.

code scenario :

let count = 0;
function increment() {
 count = count + 1;
}
increment();
setTimeout(() => {

  console.log(count);
}, 1000);

console.log(count);

Solution 1

js :

let count = 0;
function increment() {
 count = count + 1;
}
setTimeout(() => {
  increment();
  console.log(count);
}, 1000);

console.log(count);

Back to table ⬆

Javascript Practice :

Javascript fundamentals

Sum two numbers

scenario :

Write a function that takes two numbers (a and b) as argument
Sum a and b
Return the result

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a + b;
}

Back to table ⬆

Comparison operators, strict equality

scenario :

Write a function that takes two values, say a and b, as arguments
Return true if the two values are equal and of the same type

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a === b;
}

Back to table ⬆

Get type of value

scenario :

Write a function that takes a value as argument
Return the type of the value

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return typeof a;
}

Back to table ⬆

Get nth character of string

scenario :

Write a function that takes a string (a) and a number (n) as argument
Return the nth character of 'a'

code scenario :

function myFunction(a, n) {
    return 
}

Solution 1

js :

function myFunction(a, n) {
    return a[n - 1];
}

Back to table ⬆

Remove first n characters of string

scenario :

Write a function that takes a string (a) as argument
Remove the first 3 characters of a
Return the result

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(3);
}

Back to table ⬆

Get first n characters of string

scenario :

Write a function that takes a string (a) as argument
Get the first 3 characters of a
Return the result

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(0, 3);
}

Back to table ⬆

Find the position of one string in another

scenario :

Write a function that takes a string as argument
The string contains the substring 'is'
Return the index of 'is'

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.indexOf('is');
}

Back to table ⬆

Extract first half of string

scenario :

Write a function that takes a string (a) as argument
Extract the first half a
Return the result

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(0, a.length / 2);
}

Back to table ⬆

Remove last n characters of string

scenario :

Write a function that takes a string (a) as argument
Remove the last 3 characters of a
Return the result

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(0, -3);
}

Back to table ⬆

Return the percentage of a number

scenario :

Write a function that takes two numbers (a and b) as argument
Return b percent of a

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return b / 100 * a
}

Back to table ⬆

Basic JavaScript math operators

scenario :

Write a function that takes 6 values (a,b,c,d,e,f) as arguments
Sum a and b
Then substract by c
Then multiply by d and divide by e
Finally raise to the power of f and return the result
Tip: mind the order

code scenario :

function myFunction(a, b, c, d, e, f) {
    return 
}

Solution 1

js :

function myFunction(a, b, c, d, e, f) {
    return (((a + b - c) * d) / e) ** f;
}

Back to table ⬆

Check whether a string contains another string and concatenate

scenario :

Write a function that takes two strings (a and b) as arguments. If a contains b, append b to the 
beginning of a. If not, append it to the end. Return the concatenation

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a.indexOf(b) === -1 ? a + b : b + a
}

Solution 2

js :

function myFunction(a, b) {
    return a.includes(b) ? `${b}${a}` : `${a}${b}`
}

Back to table ⬆

Check if a number is even

scenario :

Write a function that takes a number as argument. If the number is even, return true. Otherwise, 
return false

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a % 2 === 0
}

Back to table ⬆

How many times does a character occur?

scenario :

Write a function that takes two strings (a and b) as arguments. Return the number of times a occurs in 
b.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return b.split(a).length - 1
}

Back to table ⬆

Check if a number is a whole number

scenario :

Write a function that takes a number (a) as argument. If a is a whole number (has no decimal place), 
return true. Otherwise, return false.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a - Math.floor(a) === 0
}

Solution 2

js :

function myFunction(a) {
    return parseInt(a) === a
}

Back to table ⬆

Multiplication, division, and comparison operators

scenario :

Write a function that takes two numbers (a and b) as arguments. If a is smaller than b, divide a by b. 
Otherwise, multiply both numbers. Return the resulting value

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a < b ? a / b : a * b
}

Back to table ⬆

Round a number to 2 decimal places

scenario :

Write a function that takes a number (a) as argument. Round a to the 2nd digit after the comma. 
Return the rounded number

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return Number(a.toFixed(2));
}

Back to table ⬆

Split a number into its digits

scenario :

Write a function that takes a number (a) as argument. Split a into its individual digits and return 
them in an array. Tipp: you might want to change the type of the number for the splitting

code scenario :

function myFunction( a ) {
    return 
}

Solution 1

js :

function myFunction( a ) {
    const string = a + '';
    const strings = string.split('');
    return strings.map(digit => Number(digit))
}

Solution 2

js :

function myFunction(a) {
    return a.toString()
            .split('')
            .map(charNum => parseInt(charNum))
}

Back to table ⬆

Javascript arrays

Get nth element of array

scenario :

Write a function that takes an array (a) and a value (n) as argument. Return the nth element of 'a'

code scenario :

function myFunction(a, n) {
    return 
}

Solution 1

js :

function myFunction(a, n) {
    return a[n - 1];
}

Back to table ⬆

Remove first n elements of an array

scenario :

Write a function that takes an array (a) as argument. Remove the first 3 elements of 'a'. Return the 
result

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(3);
}

Back to table ⬆

Get last n elements of an array

scenario :

Write a function that takes an array (a) as argument. Extract the last 3 elements of 'a'. Return the 
resulting array

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(-3);
}

Back to table ⬆

Get first n elements of an array

scenario :

Write a function that takes an array (a) as argument. Extract the first 3 elements of a. Return the 
resulting array

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.slice(0, 3);
}

Back to table ⬆

Return last n array elements

scenario :

Write a function that takes an array (a) and a number (n) as arguments. It should return the last n 
elements of a.

code scenario :

function myFunction(a, n) {
    return 
}

Solution 1

js :

function myFunction(a, n) {
    return a.slice(-n);
}

Back to table ⬆

Remove a specific array element

scenario :

Write a function that takes an array (a) and a value (b) as argument. The function should remove all 
elements equal to 'b' from the array. Return the filtered array.

code scenario :

function myFunction( a, b ) {
    return 
}

Solution 1

js :

function myFunction( a, b ) {
    return a.filter(arrItem => arrItem !== b)
}

Back to table ⬆

Count number of elements in JavaScript array

scenario :

Write a function that takes an array (a) as argument. Return the number of elements in a.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.length;
}

Back to table ⬆

Count number of negative values in array

scenario :

Write a function that takes an array of numbers as argument. Return the number of negative values 
in the array.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.filter((el) => el < 0).length;
}

Solution 2

js :

function myFunction(a) {
    const isNegative = num => num < 0;
    return a.filter(isNegative).length;
}

Back to table ⬆

Sort an array of strings alphabetically

scenario :

Write a function that takes an array of strings as argument. Sort the array elements alphabetically. 
Return the result.

code scenario :

function myFunction(arr) {
    return 
}

Solution 1

js :

function myFunction(arr) {
    return arr.sort();
}

Back to table ⬆

Sort an array of numbers in descending order

scenario :

Write a function that takes an array of numbers as argument. It should return an array with the 
numbers sorted in descending order.

code scenario :

function myFunction( arr ) {
    return 
}

Solution 1

js :

function myFunction( arr ) {
    // > 0 => sort a after b
    // < 0 => sort a before b
    // === 0 => keep original order of a and b
    return arr.sort((a, b) => b - a)
}

Back to table ⬆

Calculate the sum of an array of numbers

scenario :

Write a function that takes an array of numbers as argument. It should return the sum of the 
numbers.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return a.reduce((acc, cur) => acc + cur, 0);
}

Back to table ⬆

Return the average of an array of numbers

scenario :

Write a function that takes an array of numbers as argument. It should return the average of the 
numbers.

code scenario :

function myFunction( arr ) {
    return 
}

Solution 1

js :

function myFunction( arr ) {
    return arr.reduce((acc, cur) => acc + cur, 0) / arr.length
}

Back to table ⬆

Return the longest string from an array of strings

scenario :

Write a function that takes an array of strings as argument. Return the longest string.

code scenario :

function myFunction( arr ) {
    return 
}

Solution 1

js :

function myFunction( arr ) {
    return arr.reduce((a, b) => a.length <= b.length ? b : a)
}

Back to table ⬆

Check if all array elements are equal

scenario :

Write a function that takes an array as argument. It should return true if all elements in the array are 
equal. It should return false otherwise.

code scenario :

function myFunction( arr ) {
    return 
}

Solution 1

js :

function myFunction( arr ) {
    return new Set(arr).size === 1;
}

Back to table ⬆

Merge an arbitrary number of arrays

scenario :

Write a function that takes arguments an arbitrary number of arrays. It should return an array 
containing the values of all arrays.

code scenario :

function myFunction(...arrays) {
    return 
}

Solution 1

js :

function myFunction(...arrays) {
    return arrays.flat();
}

Back to table ⬆

Sort array by object property

scenario :

Write a function that takes an array of objects as argument. Sort the array by property b in ascending 
order. Return the sorted array

code scenario :

function myFunction(arr) {
    return 
}

Solution 1

js :

function myFunction(arr) {
    // > 0 => sort a after b
    // < 0 => sort a before b
    // === 0 => keep original order of a and b
    const sort = (x, y) => x.b - y.b;
    return arr.sort(sort);
}

Back to table ⬆

Merge two arrays with duplicate values

scenario :

Write a function that takes two arrays as arguments. Merge both arrays and remove duplicate values. 
Sort the merge result in ascending order. Return the resulting array

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return [...new Set([...a, ...b])].sort((x, y) => x - y);
}

Solution 2

js :

function myFunction(a, b) {
    let merged = a.concat(b);
    let noDuplicate = Array.from(new Set(merged));
    let sorted = noDuplicate.sort((a, b) => a - b);
    return sorted;
}

Back to table ⬆

Javascript objects

Accessing object properties one

scenario :

Write a function that takes an object with two properties as argument. It should return the value of 
the property with key country.

code scenario :

function myFunction(obj) {
    return 
}

Solution 1

js :

function myFunction(obj) {
    return obj.country;
}

Back to table ⬆

Accessing object properties two

scenario :

Write a function that takes an object with two properties as argument. It should return the value of 
the property with key 'prop-2'. Tipp: you might want to use the square brackets property accessor

code scenario :

function myFunction(obj) {
    return 
}

Solution 1

js :

function myFunction(obj) {
    return obj['prop-2'];
}

Back to table ⬆

Accessing object properties three

scenario :

Write a function that takes an object with two properties and a string as arguments. It should return 
the value of the property with key equal to the value of the string

code scenario :

function myFunction(obj, key) {
    return 
}

Solution 1

js :

function myFunction(obj, key) {
    return obj[key]
}

Back to table ⬆

Check if property exists in object

scenario :

Write a function that takes an object (a) and a string (b) as argument. Return true if the object has a 
property with key 'b'. Return false otherwise. Tipp: test case 3 is a bit tricky because the value of 
property 'z' is undefined. But the property itself exists.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    // The in operator returns true if the specified property is in 
    // the object or its prototype chain.
    return b in a;
}

Back to table ⬆

Check if property exists in object and is truthy

scenario :

Write a function that takes an object (a) and a string (b) as argument. Return true if the object has a 
property with key 'b', but only if it has a truthy value. In other words, it should not be null or 
undefined or false. Return false otherwise.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return Boolean(a[b]);
}

Solution 2

js :

function myFunction(a, b) {
    return a[b] ? true : false;
}

Back to table ⬆

Creating Javascript objects one

scenario :

Write a function that takes a string as argument. Create an object that has a property with key 'key' 
and a value equal to the string. Return the object.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return { key: a }
}

Back to table ⬆

Creating Javascript objects two

scenario :

Write a function that takes two strings (a and b) as arguments. Create an object that has a property 
with key 'a' and a value of 'b'. Return the object.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return { [a]: b }
}

Back to table ⬆

Creating Javascript objects three

scenario :

WWrite a function that takes two arrays (a and b) as arguments. Create an object that has properties 
with keys 'a' and corresponding values 'b'. Return the object.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a.reduce((acc, cur, i) => ({ ...acc, [cur]: b[i] }), {})
}

Back to table ⬆

Extract keys from Javascript object

scenario :

Write a function that takes an object (a) as argument. Return an array with all object keys.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return Object.keys(a);
}

Back to table ⬆

Return nested object property

scenario :

Write a function that takes an object as argument. In some cases the object contains other objects 
with some deeply nested properties. Return the property 'b' of object 'a' inside the original object if it 
exists. If not, return undefined

code scenario :

function myFunction(obj) {
    return 
}

Solution 1

js :

function myFunction(obj) {
    return obj?.a?.b;
}

Solution 2

js :

function myFunction(obj) {
    return obj.a && obj.a.b ? obj.a.b : undefined
}

Back to table ⬆

Sum object values

scenario :

Write a function that takes an object (a) as argument. Return the sum of all object values.

code scenario :

function myFunction(a) {
    return 
}

Solution 1

js :

function myFunction(a) {
    return Object.values(a).reduce((sum, cur) => sum + cur, 0);
}

Back to table ⬆

Remove a property from an object

scenario :

Write a function that takes an object as argument. It should return an object with all original object 
properties. except for the property with key 'b'

code scenario :

function myFunction(obj) {
    return 
}

Solution 1

js :

function myFunction(obj) {
    const { b, ...rest } = obj;
    return rest;
}

Solution 2

js :

function myFunction(obj) {
    if("b" in obj) {
        return delete obj.b && obj;
    }
}

Back to table ⬆

Merge two objects with matching keys

scenario :

Write a function that takes two objects as arguments. Unfortunately, the property 'b' in the second 
object has the wrong key. It should be named 'd' instead. Merge both objects and correct the wrong 
property name. Return the resulting object. It should have the properties 'a', 'b', 'c', 'd', and 'e'

code scenario :

function myFunction(x, y) {
    return 
}

Solution 1

js :

function myFunction(x, y) {
    const {b, ...rest} = y;
    return {...x, ...rest, d: b};
}

Solution 2

js :

function myFunction(x, y) {
    y.d = y.b;
    delete y.b;
    return {...x, ...y};
}

Back to table ⬆

Multiply all object values by x

scenario :

Write a function that takes an object (a) and a number (b) as arguments. Multiply all values of 'a' by 
'b'. Return the resulting object.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return Object.entries(a).reduce((acc, [key, val]) => {
        return { ...acc, [key]: val * b };
    }, {});
}

Back to table ⬆

Javascript dates

Check if two dates are equal

scenario :

Sounds easy, but you need to know the trick. Write a function that takes two date instances as 
arguments. It should return true if the dates are equal. It should return false otherwise.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a.getTime() === b.getTime();
}

Solution 2

js :

function myFunction(a, b) {
    return a - b === 0;
}

Back to table ⬆

Return the number of days between two dates

scenario :

Write a function that takes two date instances as argument. It should return the number of days that 
lies between those dates.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    const dif = Math.abs(a - b);
    return dif / 1000 / 60 / 60 / 24
}

Solution 2

js :

functiion myFunction(a, b) {
    return Math.abs( (a.getTime() / 86400000) - (b.getTime() / 86400000) )
}

Back to table ⬆

Check if two dates fall on the exact same day

scenario :

Write a function that takes two date instances as argument. It should return true if they fall on the 
exact same day. It should return false otherwise.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a.getFullYear() === b.getFullYear() &&
           a.getMonth() === b.getMonth() &&
           a.getDate()=== b.getDate()
}

Back to table ⬆

Check if two dates are within 1 hour from each other

scenario :

Write a function that takes two date instances as argument. It should return true if the difference between the dates is less 
than or equal to 1 hour. It should return false otherwise.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return Math.abs(a - b) / 1000 / 60 <= 60
}

Solution 2

js :

function myFunction(a, b) {
    const timeDiffLimitInMinutes = 60;
    let firstDateTime = a.getTime();
    let secondDateTime = b.getTime();
    let timeDiffInMiliSeconds = Math.abs(firstDateTime - secondDateTime);
    let timeDiffInMinutes = timeDiffInMiliSeconds / 60000;

    if(timeDiffInMinutes > timeDiffLimitInMinutes) return false;
    return true;
}

Back to table ⬆

Check if one date is earlier than another

scenario :

Write a function that takes two date instances (a and b) as arguments. It should return true if a is earlier than b. It should 
return false otherwise.

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    return a < b
}

Back to table ⬆

Javascript Sets

Check if value is present in Set

scenario :

Write a function that takes a Set and a value as arguments. Check if the value is present in 
the Set

code scenario :

function myFunction(set, val) {
    return 
}

Solution 1

js :

function myFunction(set, val) {
    return set.has(val);
}

Back to table ⬆

Convert a Set to Array

scenario :

Write a function that takes a Set as argument. Convert the Set to an Array. Return the Array

code scenario :

function myFunction(set) {
    return 
}

Solution 1

js :

function myFunction(set) {
    return [...set];
}

Back to table ⬆

Get union of two sets

scenario :

Write a function that takes two Sets as arguments. Create the union of the two sets. Return 
the result. Tipp: try not to switch to Arrays, this would slow down your code

code scenario :

function myFunction(a, b) {
    return 
}

Solution 1

js :

function myFunction(a, b) {
    const result = new Set(a);
    b.forEach((el) => result.add(el));
    return result;
}

Back to table ⬆

Creating Javascript Sets

scenario :

Write a function that takes three elements of any type as arguments. Create a Set from 
those elements. Return the result

code scenario :

function myFunction(a, b, c) {
    return 
}

Solution 1

js :

function myFunction(a, b, c) {
    const set = new Set();
    set.add(a);
    set.add(b);
    set.add(c);
    return set;
}

Back to table ⬆

Delete element from Set

scenario :

Write a function that takes a Set and a value as argument. If existing in the Set, remove the 
value from the Set. Return the result

code scenario :

function myFunction(set, val) {
    return 
}

Solution 1

js :

function myFunction(set, val) {
    set.delete(val);
    return set;
}

Solution 2

js :

function myFunction(set, val) {
    return set.has(val) ? set.delete(val) && set : set;
}

Back to table ⬆

Javascript DOM :

DOM selector methods

Select the button element on the page

scenario :

In this scenario, the existing code adds an eventListener for a click event on a variable buttonElem. It expects buttonElem to be the button element in the example UI. But, that element is not selected yet.
Assign the button element to the variable buttonElem. Click the button to verify that the code is working.
Hint: Make use of the unique id of the button element.

html :

<button type="button" id="button">OFF</button>

code scenario :

const buttonElem = 

buttonElem.addEventListener('click', () => {
  const oldText = buttonElem.innerText;
  return button.innerText = oldText === "ON" ? "OFF" : "ON";
});

Solution 1

js :

const buttonElem = document.getElementById("button");

buttonElem.addEventListener('click', () => {
  const oldText = buttonElem.innerText;
  return button.innerText = oldText === "ON" ? "OFF" : "ON";
});

Back to table ⬆

Query descendent HTML elements

scenario :

Here, the existing code expects the variables 'buttonElem' and 'inputElem' to represent the button and input elements in the example UI.
Assign the respective elements to the variables.
In this case, the two elements do not have unique identifiers - like for example an id. Instead they are direct descendents of a div element with id 'wrapper'. Use an appropriate selector method!
Click the button to verify that the code is working.

html :

<div id="wrapper">
    <input type="text" value="OFF" readonly/>
    <button type="button">Click Me</button>
</div>

code scenario :

const buttonElem = 
const inputElem = 

buttonElem.addEventListener('click', () => {
  const oldText = inputElem.value;
    return inputElem.value = oldText === "ON" ? "OFF" : "ON";
});

Solution 1

js :

const buttonElem = document.querySelector("#wrapper button");
const inputElem = document.querySelector("#wrapper input");

buttonElem.addEventListener('click', () => {
  const oldText = inputElem.value;
    return inputElem.value = oldText === "ON" ? "OFF" : "ON";
});

Back to table ⬆

Select multiple HTML elements

scenario :

In this scenario, we are looking for a list of elements gathered in one variable - rather than only one element.
Assign the list items in the view to the variable 'listItems' by using an appropriate selector method.
Once you have completed the code below, verify it by hovering over the list items until all items have the value 'ON'

html :

<ul id="list">
    <li>OFF</li>
    <li>OFF</li>
    <li>OFF</li>
    <li>OFF</li>
    <li>OFF</li>
    <li>OFF</li>
</ul>

code scenario :

const listItems = 

const handleHover = (event) => {
  return event.target.innerText = 'ON';
};

if(listItems.length > 1) {
  listItems.forEach(item => item.addEventListener('mouseover', handleHover));
}

Solution 1

js :

const listItems = document.querySelectorAll("#list li");

const handleHover = (event) => {
  return event.target.innerText = 'ON';
};

if(listItems.length > 1) {
  listItems.forEach(item => item.addEventListener('mouseover', handleHover));
}

Back to table ⬆

Events and user interactions

Execute function on button click

scenario :

The Javascript function handleText fills the input field with the words Hello World. But, there is no code to execute this function.
Complete the existing code below such that the function is called when the button is clicked. Verify by clicking the button.

html :

<input type="text" id="input" readonly/>
<button type="button" id="button">Click Me</button>

code scenario :

const button = document.getElementById('button');
const input = document.getElementById('input');

const handleClick = () => {
  input.value = 'Hello World';
};

Solution 1

js :

const button = document.getElementById('button');
const input = document.getElementById('input');

const handleClick = () => {
  input.value = 'Hello World';
};

button.addEventListener('click', handleClick);

Back to table ⬆

Execute function when cursor moves onto element

scenario :

The Javascript function changeText changes the text inside the circle. But again, there is no code to execute this function.
Complete the existing code below such that the function is called when the cursor moves onto the circle. Verify that your code works by hovering over the circle.

html :

<div id="element">
    Hover Me
</div>

code scenario :

const element = document.getElementById('element');

const changeText = () => {
  element.innerText = 'Thanks!';
};

Solution 1

js :

const element = document.getElementById('element');

const changeText = () => {
  element.innerText = 'Thanks!';
};

element.addEventListener("mouseover", changeText);

Back to table ⬆

Cursor enters and leaves element

scenario :

In this scenario we want the color of the circle to change depending on the type of cursor movement. Use the function toggleColor to turn the circle orange when the cursor moves onto it. Reuse the same function to turn it black when the cursor leaves it.
The tricky part is that you have to call toggleColor with different values for the parameter isEntering. Verify that your code is working by hovering the circle with the mouse cursor and leaving it again.

html :

<div id="element">
    Hover Me
</div>

code scenario :

const element = document.querySelector('#element');

const toggleColor = (isEntering) => {
  element.style.background = isEntering ? 'orange' : 'black';
};

Solution 1

js :

const element = document.querySelector('#element');

const toggleColor = (isEntering) => {
  element.style.background = isEntering ? 'orange' : 'black';
};

element.addEventListener('mouseover', () => toggleColor(true));
element.addEventListener('mouseleave', () => toggleColor(false));

Back to table ⬆

DOM manipulation

Remove element from the DOM

scenario :

You may not see it in the example UI, but underneath the red circle is a green circle. Extend the function removeRedCircle to remove the circle with id red from the DOM.
Make sure that you really remove the element instead of just hiding it. Confirm that your code works by clicking the button.

html :

<div id="green"/>
<div id="red"/>
<button type="button" id="button">Click Me</button>

code scenario :

const button = document.querySelector('#button');

const removeRedCircle = () => {
  
};
button.addEventListener('click', removeRedCircle);

Solution 1

js :

const button = document.querySelector('#button');

const removeRedCircle = () => {
  const redCircle = document.querySelector('#red');
  redCircle.parentNode.removeChild(redCircle);
};
button.addEventListener('click', removeRedCircle);

Solution 2

js :

const button = document.querySelector('#button');

const removeRedCircle = () => {
  document.getElementById("red").remove();
};
button.addEventListener('click', removeRedCircle);

Back to table ⬆

Change id of HTML element

scenario :

In this scenario the existing code listens to a click on the button. When the button is clicked, the function changeInput is triggered. changeInput tries to select an input field with id inputEl. But, the existing input field does not have this id. Add some Javascript code to add the id inputEl to the existing input field.
Verify that your code works by clicking the button.

html :

<div id="wrapper">
    <input type="text" placeholder="Text" readonly/>
    <button type="button">Click Me</button>
</div>

code scenario :

const button = document.querySelector('#wrapper button');

const changeInput = () => {
  const input = document.querySelector('#inputEl');
  if(input) {
    input.value = 'Hello World';
  }
};

button.addEventListener('click', changeInput);

Solution 1

js :

const button = document.querySelector('#wrapper button');

const changeInput = () => {
  const input = document.querySelector('#inputEl');
  if(input) {
    input.value = 'Hello World';
  }
};

button.addEventListener('click', changeInput);

document.querySelector('#wrapper input').setAttribute('id', 'inputEl');

Back to table ⬆

DOM fundamentals

Check the checkbox

scenario :

Your first JavaScript DOM exercise. Let's start simple.
Extend the JavaScript code below to interact with the displayed HTML elements. Once you click the button, the checkbox should be checked.
Confirm your code by clicking the button!

html :

<input id="checkbox" disabled/>
<label for="checkbox">checkbox</label>
<button type="button" id="button">Verify Code</button>

code scenario :

const button = document.getElementById('button');
button.addEventListener('click', () => {
  
});

Solution 1

js :

const button = document.getElementById('button');
button.addEventListener('click', () => {
  const checkbox = document.getElementById('checkbox');
  checkbox.checked = true;
});

Back to table ⬆

Get full-name from input

scenario :

Extend the JavaScript code below to interact with the displayed HTML elements.
This time we are looking for the full name. When the button is clicked, combine the names of the first two input fields. Insert the full name in the third input field.
Hint: Check if your code still works if you change the first or last name.
Confirm your code by clicking the button!

html :

<input type="text" id="firstName" placeholder="Max" value="Max"/>
<input type="text" id="lastName" placeholder="Musterman" value="Musterman"/>
<input type="text" id="fullName" placeholder="full name" readonly/>
<button type="button" id="button">Verify Code</button>

code scenario :

const button = document.getElementById('button');
button.addEventListener('click' , () => {
  
});

Solution 1

js :

const button = document.getElementById('button');
button.addEventListener('click' , () => {
  const firstName = document.getElementById('firstName');
  const lastName = document.getElementById('lastName');
  const fullName = document.getElementById('fullName');
  fullName.value = firstName.value + ' ' + lastName.value;
});

Back to table ⬆

Pop the balloons

scenario :

Make the balloons pop by hovering over them.
Extend the JavaScript code below to interact with the displayed HTML elements. Every time you hover over a balloon, it should become invisible.
Your goal is to pop all the balloons one after the other.

html :

<ul id="list">
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
  <li/>
</ul>

code scenario :

const list = document.getElementById('list');

Solution 1

js :

const list = document.getElementById('list');
const handleHover = event => {
  if(event.target !== list) {
    event.target.style.visibility = 'hidden';
  }
};

list.addEventListener('mouseover', handleHover);

Back to table ⬆

Recursive functions

Stop and restart the moving button

scenario :

This is a good exercise to learn about recursive functions. The function move in the code below moves the button 1px to the left or the right. It is recursive because it calls itself again and again. This keeps the button moving.
Extend the JavaScript code. Once you click the button, it should stop moving. When you click it again, it should move again.
Confirm your code by clicking the button twice.

html :

<button type="button" id="button">Click Me</button>

code scenario :

const button = document.getElementById('button');
let stopped = false;
 
function move(isReturning) {
 const width = button.parentNode.clientWidth;
 const left = parseInt(button.style.left , 10) || 0;
 if (!stopped) {
    button.style.left = (isReturning ? left - 1 : left + 1) + 'px';
    setTimeout(() => move ((isReturning && left > 0) || left === width - button.clientWidth), 10);
 };
};
 
move();
 
button.addEventListener('click', () => {
  
});

Solution 1

js :

const button = document.getElementById('button');
let stopped = false;
 
function move(isReturning) {
 const width = button.parentNode.clientWidth;
 const left = parseInt(button.style.left , 10) || 0;
 if (!stopped) {
    button.style.left = (isReturning ? left - 1 : left + 1) + 'px';
    setTimeout(() => move ((isReturning && left > 0) || left === width - button.clientWidth), 10);
 };
};
 
move();
 
button.addEventListener('click', () => {
  stopped = !stopped;
  move();
});

Back to table ⬆

Files

README.md

Latest commit

History

README.md

File metadata and controls

Welcome ! 👋

What is JSchallenger ? 🙂

Why this repo ? 😶

Table of solutions

Javascript Basics :

variables

Reassign a value to a variable

Assign a value to a variable

Assign the value of another variable

Create the missing variable

Accessing a variable 1

Accessing a variable 2

Declare a variable and assign a number

Reassign a value to a variable 2

booleans

Assign boolean to a variable

Convert Number to Boolean

operators

Comparison operators - Equal

Comparison operators - Not Equal

Comparison operators - Greater than

Comparison operators - Less than

Comparison operators - Greater than or equal

Comparison operators - Less than or equal

strings

Create a Javascript string

Different ways to create Javascript strings

Connect Javascript strings 1

conditionals

if statement - satisfy condition

if statement - add missing condition

functions I

Function declaration

Function expression

Correctly return value from function 1

Correctly return value from function 2

arrays

loops

asynchronous javascript

Execute the code synchronously

Execute the code asynchronously

Javascript Practice :

Javascript fundamentals

Sum two numbers

Comparison operators, strict equality

Get type of value

Get nth character of string

Remove first n characters of string

Get first n characters of string

Find the position of one string in another

Extract first half of string

Remove last n characters of string

Return the percentage of a number

Basic JavaScript math operators

Check whether a string contains another string and concatenate

Check if a number is even

How many times does a character occur?

Check if a number is a whole number

Multiplication, division, and comparison operators

Round a number to 2 decimal places

Split a number into its digits

Javascript arrays

Get nth element of array

Remove first n elements of an array

Get last n elements of an array

Get first n elements of an array

Return last n array elements

Remove a specific array element

Count number of elements in JavaScript array

Count number of negative values in array

Sort an array of strings alphabetically

Sort an array of numbers in descending order

Calculate the sum of an array of numbers

Return the average of an array of numbers