This is a TypeScript library that provides a set of utility functions for type guarding. Type guarding allows you to perform runtime checks on values to determine if they satisfy certain conditions. The library offers various functions to check and validate types, create literal type guards, validate arrays and tuples, and more.

npm install @lickle/is

• string
• object
• number
• undef
• func
• nul
• literal<T extends any>(of: T)
• array<T = any>(of?: Guard<T>)
• tuple<T extends Guard<any>[]>(...of: T)
• record<K extends string = string, V = any>(key?: Guard<K>, value?: Guard<V>)
• struct<T extends Record<any, Guard<any>>>(of: T, strict: boolean = true)
• defined<T>(x: T | undefined | null): x is T
• or<T extends Guard<any>[]>(...of: T)
• is<T extends V, V = unknown>(cb: (x: V) => boolean): Guard<T, V>
• Guard<T extends V, V = unknown>
• TypeOfGuard<G>

Install the library using npm or yarn:

npm install my-type-guards-library

import { tp } from '@lickle/is'

const unknown: unknown

if (tp.string(unknown)) return // string

if (tp.number(unknown)) return // number

if (tp.array()(unknown)) return // unknown[]

if (tp.array(tp.string)(unknown)) return // string[]

if (tp.record()(unknown)) return // Record<string, any>

if (tp.record(tp.literal('foo'), tp.number)(unknown)) return // { foo: number }

if (tp.tuple(tp.literal('foo'), tp.literal(10))(unknown)) return // ['foo', 10]

if (tp.struct({ foo: tp.literal('bar') })(unknown)) return // { foo: 'bar' }

if (tp.or(tp.literal('foo'), tp.literal('bar'))(unknown)) return // 'foo' | 'bar'

const items: (number | null)[]
const defined = items.filter(tp.defined) // number[]

A type guard function that checks if a value is of type string.

A type guard function that checks if a value is of type object.

A type guard function that checks if a value is of type number.

A type guard function that checks if a value is undefined.

A type guard function that checks if a value is of type Function.

A type guard function that checks if a value is null.

The literal function creates a type guard that checks if a value is equal to a specific literal value.

The array function checks if a value is an array and optionally checks if all elements of the array match a given type guard.

The tuple function checks if a value is an array with elements that match the specified guards.

The record function checks if a given value is a valid record object, with optional key and value guards.

The struct function is a type guard that checks if an object matches a given structure defined by a record of guards.

The defined function checks if a value is defined (not undefined or null) and returns a boolean.

The or function allows you to check if a value matches any of the provided guards.

The is function is a TypeScript type guard that checks if a value satisfies a given condition. It takes a callback function cb that takes a value of type V and returns a boolean value. The callback function is used to define the condition for type guarding.

A type alias representing a TypeScript type guard function. It takes a value of type V and returns a boolean indicating whether the value is of type T.

A conditional type that extracts the guarded type from a Guard function.

MIT © Dan Beaven