Is-lite NPM | npm.io

is-lite

Lightweight type check tool.

Typescript ready with type guards to infer the correct type inside conditionals.

Setup

npm install is-lite

Usage

import is from 'is-lite';

is('value'); // string
is.string('value'); // true

You can also import any checker individually since 1.0

import { isString } from 'is-lite/exports';

isString('value'); // true

API

is(value)
Returns the type of the value.

Primitives are lowercase: bigint, boolean, null, number, string, symbol, undefined. The rest are camelcase: Array, Function, GeneratorFunction, Object, ...

is.array(value)

is.arrayOf(target: any[], predicate: (value: unknown) => boolean)
Check if all items in an array are of the same type.

is.arrayOf(['a', 'b'], is.string); // true
is.arrayOf([123, 456], is.nnumber); // true

is.arrayOf(['a', 1], is.string); // false

is.asyncFunction(value)
Check if the value is an async function that can be called with await.

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

is.asyncGeneratorFunction(value)

is.bigint(value)

is.boolean(value)

is.date(value)

is.defined(value)
Check if the value is anything but undefined.

is.domElement(value)
Check if the value is a DOM Element.

is.empty(value)
Returns true if:

the value is a string, and the length is 0
the value is an Object and Object.keys(value).length is 0
the value is an Array, and the length is 0
the value is a Map, and the size is 0
the value is a Set, and the size is 0

is.error(value)

is.function(value)

is.generator(value)
Check for an object that has its own .next() and .throw() methods and has a function definition for Symbol.iterator

is.generatorFunction(value)

is.instanceOf(value, class)
Check if the value is a direct instance of the class.

class APIError extends Error {}

const error = new APIError('Fail');

is.instanceOf(error, APIError); // true
is.instanceOf(error, Error); // false

is.iterable(value)

is.map(value)

is.nan(value)

is.null(value)

is.nullOrUndefined(value)

is.number(value)
Note: is.number(NaN) returns false

is.numericString(value)
Check for a string that represents a number.

is.numericString('42'); // true
is.numericString('-5'); // true
is.numericString('Inifinity'); // true
is.numericString('NaN'); // true

is.plainFunction(value)
Check if the value is a function (it doesn't include async and generator functions)

is.primitive(value)

is.object(value)
Remember that functions and arrays are objects too.

is.oneOf(target: any[], value: any)
Check if the value exists in the target

const colors = ['red', 'green', 'blue'];

is.oneOf(colors, 'green'); // true
is.oneOf(colors, 'brown'); // false

is.plainObject(value)
Check if the object is created by either {}, new Object() or Object.create(null).

is.promise(value)

is.propertyOf(target: object, key: string, predicate?: (value: unknown) => boolean)
Check if the key exists in the target. If you pass a predicate function, it will check the value's type.

const map = { items: [1], isLogged: false, retries: 0 };

is.propertyOf(map, 'retries'); // true
is.propertyOf(map, 'auth'); // false

is.propertyOf(map, 'retries', is.number); // true
is.propertyOf(map, 'items', is.array); // true
is.propertyOf(map, 'isLogged', is.string); // false

is.regexp(value)

is.set(value)

is.string(value)

is.symbol(value)

is.undefined(value)

is.weakMap(value)

is.weakSet(value)