@wicle/is

JavaScript and TypeScript type testing library uniquely identifying types without overlap.

It does type testing for the following types:

• Array
• Object
• Function
• String
• Number
• Date
• RegExp
• Error
• Symbol
• Map
• WeakMap
• Set
• WeakSet
• Class
• Promise
• AsyncFunction
• Glob

If a variable is one of the above types, it means it is not of any other types above. For example, if a variable is of type Function, then it is not of type Object. A class instance is of type Object, but not of type Class or Function, etc.

Installation

npm install @wicle/is

# or
yarn add @wicle/is

# or
pnpm add @wicle/is

Usage

import is from '@wicle/is'

function processValue(arg) {
    if (is.isFunction(arg)) {
        // Handle function
        arg()
    } else if (is.isClass(arg)) {
        // Handle class constructor
        const instance = new arg()
    } else if (is.isString(arg)) {
        // Handle string
        console.log(arg.toUpperCase())
    }
    // ... handle other types
}

API

All functions return true if the value matches the specified type, false otherwise.

• is.isArray(arg) - Tests if value is an Array
• is.isObject(arg) - Tests if value is a plain Object
• is.isFunction(arg) - Tests if value is a Function (excluding classes and async functions)
• is.isString(arg) - Tests if value is a String
• is.isNumber(arg) - Tests if value is a Number
• is.isDate(arg) - Tests if value is a Date
• is.isRegExp(arg) - Tests if value is a RegExp
• is.isError(arg) - Tests if value is an Error
• is.isSymbol(arg) - Tests if value is a Symbol
• is.isMap(arg) - Tests if value is a Map
• is.isWeakMap(arg) - Tests if value is a WeakMap
• is.isSet(arg) - Tests if value is a Set
• is.isWeakSet(arg) - Tests if value is a WeakSet
• is.isClass(arg) - Tests if value is a Class constructor
• is.isPromise(arg) - Tests if value is a Promise-like object
• is.isAsyncFunction(arg) - Tests if value is an async function
• is.isGlob(arg) - Tests if value is a glob pattern (string or array of strings)

Important Notes

Class vs Object vs Function

This library makes clear distinctions between:

• Class: A class constructor/definition
• Function: A regular function (not a class or async function)
• Object: A plain object or class instance

class MyClass {}
const myFunction = () => {}
const myObject = {}
const myInstance = new MyClass()

is.isClass(MyClass) // true
is.isFunction(MyClass) // false
is.isObject(MyClass) // false

is.isFunction(myFunction) // true
is.isClass(myFunction) // false
is.isObject(myFunction) // false

is.isObject(myObject) // true
is.isClass(myObject) // false
is.isFunction(myObject) // false

is.isObject(myInstance) // true (class instances are objects)
is.isClass(myInstance) // false
is.isFunction(myInstance) // false

Type Safety

All functions provide TypeScript type guards for better type safety:

function processValue(value: unknown) {
    if (is.isString(value)) {
        // TypeScript now knows 'value' is a string
        console.log(value.toUpperCase())
    }

    if (is.isArray(value)) {
        // TypeScript now knows 'value' is an array
        console.log(value.length)
    }
}