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1.0.5 • Public • Published

required-parameters-js : Mandatory function parameters for JS

This tiny package allows you to use the required identifier (as a default parameter value) on those function parameters that you want to be mandatory. If any of those parameters are not provided, a Missing required parameter Error is thrown. s Compatible with Node & Browsers

Usage Example

  /* global required */
  import './required-parameters.js'; 
  // or in Node...
  // require('required-parameters');
  // declare a function with a required parameter
  function myFunc( myParam = required ){
    /* function code... */
  // Uncaught Error : Missing required parameter 
  // at myFunc (https://localhost/main.js/:10:5)

Distribution & installation

You can use any of the following alternatives:

- NPM : Install with npm :

$ npm install required-parameters-js -s

- GIT : Clone with git :

$ git clone

-ZIP : Download the package in a ZIP file from :


- CDN: Use the CDN to include the latest version of the library in your document head :

Warning: Not recommended in production enviroments :

<script src="">


This package is shipped with support to Node CommonJS and ES6 Modules. Use the appropiate method accoordintg to your enviroment.

  // ES6 Module Import : 
  import './required-parameters.js'; 
  // CommonJS Node Import :

Code Linters

Because the required keyword is declared by the library in the global scope your linter will complain when detecting that required is used without previous explicit declaration in your specific namespace. To disable the warning set the require keyword in your linter config file or inlined in your code use :

/* global required */

How it works

- Short story short :

Because a line of code is worth a thousand words...

const required = ()=>{ throw new Error('Required Parameter!') };
function myFunc( myParamater = required() ){ /**/ }

Involve a getter for required and you have it... your own implementation of required parameters ;)

- Short story long :

Required-param performs its magic using the ES6 function default parameter values.

First the required identifier is declared by this library in the corresponding global object (window | self | global), to ensure it can be used anywhere (Browser main thread, Modules, Workers or Node).

When you call a function that uses required in any of its parameters, and the required parameter is missing, the javascript interpreter tries to assign the value of required to the argument.

Because the required variable value retrieval attemps, are handled internally by a getter, the getter function only needs to throw an Error.


npm i required-parameters-js

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