map-foreach.md

map and forEach are both array methods in JavaScript that iterate over an array.

Array.prototype.map()

map creates a new array by calling a provided function on every element in the calling array.

let numbers = [1, 2, 3, 4, 5];
let squares = numbers.map(num => num * num);
console.log(squares); // [1, 4, 9, 16, 25]

Pros:

• It returns a new array, leaving the original array unchanged, which is in line with functional programming principles.
• It always returns a new array of the same length as the input array.

Cons:

• It's not efficient if you're not using the returned array, because it always returns a new array.

Array.prototype.forEach()

forEach executes a provided function once for each array element. It does not return anything.

let numbers = [1, 2, 3, 4, 5];
numbers.forEach((num, index) => {
    console.log(`Number ${num} is at index ${index}`);
});

Pros:

• It's useful for applying a function to every element in an array for side effects (like logging or updating the DOM).
• It doesn't return a new array, so it's more efficient than map if you don't need a new array.

Cons:

• It doesn't return anything, so you can't chain other array methods after it.
• It alters the original array (if you change elements), which is not in line with functional programming principles.

In summary, use map when you want to transform elements in an array and use the result. Use forEach when you want to apply a function to each element in an array for side effects.