is 

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

Install

``
$ npm install @sindresorhus/is
`

Usage

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

is('🦄');
//=> 'string'

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

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

API

$3

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').

$3

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.

##### .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.

##### .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)

##### .arrayLike(value)

A value is array-like if it is not a function and has a value.length that is a safe integer greater than or equal to 0.

`js
is.arrayLike(document.forms);
//=> true

function () {
is.arrayLike(arguments);
//=> true
}
`

##### .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

$3

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 - Check if something is a Node.js stream
- is-observable - Check if a value is an Observable
- file-type - Detect the file type of a Buffer/Uint8Array
- is-ip - Check if a string is an IP address
- is-array-sorted - Check if an Array is sorted
- is-error-constructor - Check if a value is an error constructor
- is-empty-iterable - Check if an Iterable is empty
- is-blob - Check if a value is a Blob - File-like object of immutable, raw data
- has-emoji - Check whether a string has any emoji

Created by

- Sindre Sorhus
- Giora Guttsait
- Brandon Smith

License

MIT