CheckType.of()

Why did I create this?

Because in JavaScript, (almost) everything is an object:

typeof {}; // -> 'object' - totally agree
typeof []; // -> 'object' - are you sure?
typeof new Date(); // -> 'object' - ok, kind of makes sense because class instances are objects in JS, but it's useless
typeof null; // -> 'object' - what?
typeof undefined; // -> 'undefined' - finally something normal
typeof NaN; // -> 'number' - how? it's in the name

And to add more complex type checking:

// ES6 class
class A {}
typeof A; // -> 'function'
CheckType.of(A).type; // -> 'class'

// ES5 class
function B() {}
B.prototype.someMethod = function () {};
typeof B; // -> 'function'
CheckType.of(B).type; // -> 'class'

// Don't worry, these still work as expected:
CheckType.of(() => {}).type; // -> 'function'
CheckType.of(function () {}).type; // -> 'function'

Usage / Examples

Import the CheckType class without instantiating it; just use CheckType.of(item) to access all the methods.

import { CheckType, TItemType } from '@danielvigaru/check-type-of';

Using the type property

Get the type of an item by accessing the type: TItemType property:

typeof []; // -> 'object'
CheckType.of([]).type; // -> 'array'

See how it says 'array' and not 'object'? Yeah.

Using the is... and isNot... methods

These methods take a callback as a parameter and execute it if the item being checked matches the specified type. You can chain multiple is... methods.

1. Use is... and isNot... methods like you would use if/else statements:

CheckType.of(new Date())
    .isDate(() => console.log("Looks like we've got ourselves a date!"))
    .isNotDate(() => console.log('This is anything but a date'));

// Output: "Looks like we've got ourselves a date!"

Note: You can't chain multiple isNot... methods because it wouldn't make sense; it would execute all/most of them each time.

2. Chain multiple methods like you would in a switch statement:

CheckType.of(someUnknownVariable)
    .isNumber(() => console.log("'It's a number"))
    .isDate(() => console.log("Looks like we've got ourselves a date!"))
    .isArray(() => console.log("['A', 'r', 'r', 'a', 'y']"));

Method Reference

All of these methods have an isNot... counterpart.

Method	Executes the callback if the item is:	.type property
isArray	[], instanceof Array	'array'
isBoolean	true, false	'boolean'
isClass	ES5 class, ES6 class	'class'
isDate	instanceof Date	'date'
isFunction	a function that isn't an ES5 class	'function'
isMap	instanceof Map	'map'
isNull	null	'null'
isNullish*	null, undefined	-
isNumber	a number: decimal, octal, hex, binary, float	'number'
isObject	{}, instanceof Object	'object'
isString	a string	'string'
isUndefined	undefined	'undefined'

* Utility method that does not assign a value to the .type property.