How to Create an Async Function via “new Function”

By  on  

One thing I love about JavaScript is that there are many ways to accomplish the same task, one such example being creating functions. There are several patterns for functions; one of the last you see used is the new Function method:

/* new Function(arg1, arg2 (...), body) */
const myFunction = new Function('users', 'salary', 'return users * salary');

What if you want to use this new Function method to create an async function? You need to be a bit clever, and thanks to MDN, we have an answer:

// Shim for allowing async function creation via new Function
const AsyncFunction = Object.getPrototypeOf(async function(){}).constructor;

// Usage
const fetchPage = new AsyncFunction("url", "return await fetch(url);");
fetchPage("/").then(response => { ... });

The usage of Object.getPrototypeOf(async function(){}).constructor is super clever, as a native AsyncFunction doesn't exist. I don't believe that I've ever used the new Function pattern but that doesn't mean you don't! And now you can make them asynchronous!

Recent Features

  • By
    JavaScript Promise API

    While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready?  Promises are becoming a big part of the JavaScript world...

  • By
    39 Shirts – Leaving Mozilla

    In 2001 I had just graduated from a small town high school and headed off to a small town college. I found myself in the quaint computer lab where the substandard computers featured two browsers: Internet Explorer and Mozilla. It was this lab where I fell...

Incredible Demos

Discussion

  1. Gustavo

    fetch() is already an async function, can you change your example?

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!