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
    An Interview with Eric Meyer

    Your early CSS books were instrumental in pushing my love for front end technologies. What was it about CSS that you fell in love with and drove you to write about it? At first blush, it was the simplicity of it as compared to the table-and-spacer...

  • By
    7 Essential JavaScript Functions

    I remember the early days of JavaScript where you needed a simple function for just about everything because the browser vendors implemented features differently, and not just edge features, basic features, like addEventListener and attachEvent.  Times have changed but there are still a few functions each developer should...

Incredible Demos

  • By
    Record Text Selections Using MooTools or jQuery AJAX

    One technique I'm seeing more and more these days (CNNSI.com, for example) is AJAX recording of selected text. It makes sense -- if you detect users selecting the terms over and over again, you can probably assume your visitors are searching that term on Google...

  • By
    CSS Filters

    CSS filter support recently landed within WebKit nightlies. CSS filters provide a method for modifying the rendering of a basic DOM element, image, or video. CSS filters allow for blurring, warping, and modifying the color intensity of elements. Let's have...

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!