CheckType.of()


Why did I create this?

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

``javascript
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:

`javascript
// 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.

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

$3

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

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

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

$3

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:

`javascript
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:

`javascript
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.