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JS type check (TypeScript supported) functions like `isObject() isArray()` etc. A simple & small integration.
The is-what npm package provides utility functions to check the type of a given value. It helps in determining whether a value is an object, array, function, string, number, etc. This can be particularly useful in type-checking scenarios and ensuring that values conform to expected types.
isObject
The isObject function checks if a given value is a plain object. It returns true for plain objects and false for arrays and other types.
const { isObject } = require('is-what');
console.log(isObject({})); // true
console.log(isObject([])); // false
isArray
The isArray function checks if a given value is an array. It returns true for arrays and false for other types.
const { isArray } = require('is-what');
console.log(isArray([])); // true
console.log(isArray({})); // false
isFunction
The isFunction function checks if a given value is a function. It returns true for functions and false for other types.
const { isFunction } = require('is-what');
console.log(isFunction(function() {})); // true
console.log(isFunction({})); // false
isString
The isString function checks if a given value is a string. It returns true for strings and false for other types.
const { isString } = require('is-what');
console.log(isString('hello')); // true
console.log(isString(123)); // false
isNumber
The isNumber function checks if a given value is a number. It returns true for numbers and false for other types.
const { isNumber } = require('is-what');
console.log(isNumber(123)); // true
console.log(isNumber('123')); // false
Lodash is a popular utility library that provides a wide range of functions for manipulating arrays, objects, and other types. It includes type-checking functions similar to is-what, such as _.isObject, _.isArray, _.isFunction, _.isString, and _.isNumber. Lodash offers more comprehensive functionality beyond type-checking.
Underscore is another utility library that provides functional programming helpers for working with arrays, objects, and other types. It includes type-checking functions like _.isObject, _.isArray, _.isFunction, _.isString, and _.isNumber. Underscore is similar to Lodash but with a smaller footprint and fewer features.
Type-detect is a simple library for detecting the type of a given value. It provides functions like typeDetect(value) which returns a string representing the type of the value. While it offers similar functionality to is-what, it focuses on returning type names rather than boolean checks.
npm i is-what
Very simple & small JS type check functions. It's fully TypeScript supported!
Motivation: I built is-what because the existing solutions were all too complex.
isString, isNumber, isBoolean, isObject, isFunction, isArray, isUndefined, isNull, isRegExp, isDate, isSymbol, isPrimitive, isType, getType
is-what is really easy to use, and all functions above work just like you'd expect.
import { isString, isType, getType } from 'is-what'
isString('') // returns true
isType('', String) // returns true
getType('') // returns 'String'
Checking for isNumber
and isDate
will return false
if the payload is NaN
or an invalid date. This is done intentionally and especially useful when you need to check if numbers or dates are correct in your functions!
isNumber(NaN) // returns false
isDate(new Date('---- invalid date ----')) // returns false
is-what makes TypeScript know the type during if statements. This means that a check returns the type of the payload for TypeScript users.
function isNumber (payload: any): payload is number {
// return boolean
}
// As you can see above, all functions return a boolean for JavaScript, but pass the payload type to TypeScript.
// usage example:
function fn (payload: string | number): number {
if (isNumber(payload)) {
// ↑ TypeScript already knows payload is a number here!
return payload
}
}
isObject
with TypeScript will declare the payload to be an object type with any props:
function isObject (payload: any): payload is {[key: any]: any} {
return isObject(payload)
}
// The reason to return `{[key: any]: any}` is to be able to do
if (isObject(payload) && payload.id) return payload.id
// if isObject() would return `payload is object` then it would give an error at `payload.id`
If you want more control over which kind of objects are allowed you can use isObjectLike<T>
:
function isObjectLike<T extends object> (payload: any): payload is T {
return isObject(payload)
}
// usage examples:
isObjectLike<{specificKey: string}>(payload)
isObjectLike<object>(payload)
// you can just pass a specific type for TS to check on.
It's litterally just these functions:
function getType (payload) {
return Object.prototype.toString.call(payload).slice(8, -1)
}
function isUndefined (payload) {
return getType(payload) === 'Undefined'
}
function isString (payload) {
return getType(payload) === 'String'
}
function isObject (payload) {
return getType(payload) === 'Object'
}
// etc...
See the full source code here.
npm run test
FAQs
JS type check (TypeScript supported) functions like `isPlainObject() isArray()` etc. A simple & small integration.
The npm package is-what receives a total of 5,229,554 weekly downloads. As such, is-what popularity was classified as popular.
We found that is-what demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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