is/readme.md

# is [![Build Status](https://travis-ci.org/sindresorhus/is.svg?branch=master)](https://travis-ci.org/sindresorhus/is)

> Type check values: `is.string('🦄') //=> true`

<img src="header.gif" width="182" align="right">


## Install

```
$ npm install @sindresorhus/is
```


## Usage

```js
const is = require('@sindresorhus/is');

is('🦄');
//=> 'string'

is(new Map());
//=> 'Map'

is.number(6);
//=> true
```


## API

### is(value)

Returns the type of `value`.

Primitives are lowercase and object types are camelcase.

Example:

- `'undefined'`
- `'null'`
- `'string'`
- `'symbol'`
- `'Array'`
- `'Function'`
- `'Object'`

Note: It will throw if you try to feed it object-wrapped primitives, as that's a bad practice. For example `new String('foo')`.

### is.{method}

All the below methods accept a value and returns a boolean for whether the value is of the desired type.

#### Primitives

##### .undefined(value)
##### .null(value)
##### .string(value)
##### .number(value)
##### .boolean(value)
##### .symbol(value)

#### Built-in types

##### .array(value)
##### .function(value)
##### .buffer(value)
##### .object(value)

Keep in mind that [functions are objects too](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions).

##### .regExp(value)
##### .date(value)
##### .error(value)
##### .nativePromise(value)
##### .promise(value)

Returns `true` for any object with a `.then()` and `.catch()` method. Prefer this one over `.nativePromise()` as you usually want to allow userland promise implementations too.

##### .generator(value)

Returns `true` for any object that implements its own `.next()` and `.throw()` methods and has a function definition for `Symbol.iterator`.

##### .generatorFunction(value)

##### .asyncFunction(value)

Returns `true` for any `async` function that can be called with the `await` operator. 

```js
is.asyncFunction(async () => {});
// => true

is.asyncFunction(() => {});
// => false
```

##### .map(value)
##### .set(value)
##### .weakMap(value)
##### .weakSet(value)

#### Typed arrays

##### .int8Array(value)
##### .uint8Array(value)
##### .uint8ClampedArray(value)
##### .int16Array(value)
##### .uint16Array(value)
##### .int32Array(value)
##### .uint32Array(value)
##### .float32Array(value)
##### .float64Array(value)

#### Structured data

##### .arrayBuffer(value)
##### .sharedArrayBuffer(value)
##### .dataView(value)

#### Miscellaneous

##### .truthy(value)

Returns `true` for all values that evaluate to true in a boolean context:

```js
is.truthy('🦄');
//=> true

is.truthy(undefined);
//=> false
```

##### .falsy(value)

Returns `true` if `value` is one of: `false`, `0`, `''`, `null`, `undefined`, `NaN`. 

##### .nan(value)
##### .nullOrUndefined(value)
##### .primitive(value)

JavaScript primitives are as follows: `null`, `undefined`, `string`, `number`, `boolean`, `symbol`.

##### .integer(value)

##### .safeInteger(value)

Returns `true` if `value` is a [safe integer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger).

##### .plainObject(value)

An object is plain if it's created by either `{}`, `new Object()`, or `Object.create(null)`.

##### .iterable(value)
##### .class(value)

Returns `true` for instances created by a ES2015 class.

##### .typedArray(value)

##### .inRange(value, range)

Check if `value` (number) is in the given `range`. The range is an array of two values, lower bound and upper bound, in no specific order.

```js
is.inRange(3, [0, 5]);
is.inRange(3, [5, 0]);
is.inRange(0, [-2, 2]);
```

##### .inRange(value, upperBound)

Check if `value` (number) is in the range of `0` to `upperBound`.

```js
is.inRange(3, 10);
```

##### .domElement(value)

Returns `true` if `value` is a DOM Element.

##### .infinite(value)

Check if `value` is `Infinity` or `-Infinity`.

##### .even(value)

Returns `true` if `value` is an even integer.

##### .odd(value)

Returns `true` if `value` is an odd integer.

##### .empty(value)

Returns `true` if `value` is falsy or an empty string, array, object, map, or set.

##### .emptyOrWhitespace(value)

Returns `true` if `is.empty(value)` or a string that is all whitespace.


##### .any(predicate, ...values)

Returns `true` if **any** of the input `values` returns true in the `predicate`:

```js
is.any(is.string, {}, true, '🦄');
//=> true

is.any(is.boolean, 'unicorns', [], new Map());
//=> false
```

##### .all(predicate, ...values)

Returns `true` if **all** of the input `values` returns true in the `predicate`:

```js
is.all(is.object, {}, new Map(), new Set());
//=> true

is.all(is.string, '🦄', [], 'unicorns');
//=> false
```

## FAQ

### Why yet another type checking module?

There are hundreds of type checking modules on npm, unfortunately, I couldn't find any that fit my needs:

- Includes both type methods and ability to get the type
- Types of primitives returned as lowercase and object types as camelcase
- Covers all built-ins
- Unsurprising behavior
- Well-maintained
- Comprehensive test suite

For the ones I found, pick 3 of these.

The most common mistakes I noticed in these modules was using `instanceof` for type checking, forgetting that functions are objects, and omitting `symbol` as a primitive.


## Related

- [is-stream](https://github.com/sindresorhus/is-stream) - Check if something is a Node.js stream
- [is-observable](https://github.com/sindresorhus/is-observable) - Check if a value is an Observable
- [file-type](https://github.com/sindresorhus/file-type) - Detect the file type of a Buffer/Uint8Array
- [is-ip](https://github.com/sindresorhus/is-ip) - Check if a string is an IP address
- [is-array-sorted](https://github.com/sindresorhus/is-array-sorted) - Check if an Array is sorted
- [is-error-constructor](https://github.com/sindresorhus/is-error-constructor) - Check if a value is an error constructor
- [is-empty-iterable](https://github.com/sindresorhus/is-empty-iterable) - Check if an Iterable is empty
- [is-blob](https://github.com/sindresorhus/is-blob) - Check if a value is a Blob - File-like object of immutable, raw data


## Created by

- [Sindre Sorhus](https://github.com/sindresorhus)
- [Giora Guttsait](https://github.com/gioragutt)


## License

MIT