What is a Noop in Javascript?

A noop in javascript usually refers to a function that does nothing and returns nothing (undefined). It looks something like this:

const noop = () => {}

Noops in Javascript are often used as a function placeholder. There is no “true noop” (machine instruction code) in Javascript, instead Javascript noops are a convention. The convention became widespread alongside the development of plugins for cross-browser UI libraries such as jQuery. JS noops gave library developers a way to create placeholders for user-defined functions or hooks.

When to use a Noop?

Noops in Javascript are used to create more concise and legible code when you are building a library other developers will use in their programs and that library surfaces an option for developer-supplied functions.

For example, if you’re building a plugin that validates form inputs as the end-user types, you might provide an optional configuration for a developer-supplied function that gets called when validation fails. The basic implementation could look like this:

// inputElement is a form input DOM node
validate(inputElement, {rules: [{type: 'number'}], onFail: () => alert('Oh no!') })

And the library internals might be implemented like this:

function validate(element, options) {
    ...

    const onFail = options.onFail || noop

    function validate(input, rules) {
        if (rules.every(r => evaluateRule(input, r)) === false) {
            // regardless of whether the function has been defined by the user, calling onFail won't throw an error
            onFail()
        }
    }

    ...
}

As you can see in the above example, whether or not the onFail function is supplied, the library implementation won’t throw an error. The implementation could also omit the onFail function, in which case the noop would get called:

validate(inputElement, {rules: [{type: 'number'}]})

An alternative approach would involve checking the value of the onFail variable each place it’s used. Using a noop the library developer ensures the value of the optional hooks are always functions.

Library-specific Noops

Several popular JS libraries come with their own noop implementation. They all do nothing and return undefined:

• Angular
• jQuery
• Lodash

Other Javascript Noops

Javascript, being the exciting language that it is, has many ways to express logical nothingness. To understand why one might want to use these expressions is beyond the scope of this article. However, here are a few possible non-function noop implementations in Javascript:

null
false
0
;
undefined
{}

Launch Javascript Apps Quickly with Noop Templates

The Noop developer platform created several App Templates to get up and running with a Javascript project both locally and in deployed environments.

• Svelte
• Vue
• Astro
• Next.js