What is the JavaScript convention for no operation?

To answer the original question, the most elegant and neat implementation of a noop function in pure Javascript (as is also discussed here) is Function.prototype. This is because:

1. Function.prototype is a function:

typeof Function.prototype === "function" // returns true

2. It can be invoked as a function and essentially does nothing as shown here:

setTimeout(function() {
      console.log('Start: ', Date.now());
      Function.prototype();
      console.log('End  : ', Date.now());
    }, 1000);

Although this is a “true noop” since most browsers seem to do nothing to execute the noop defined this way (and hence save CPU cycles), there might be some performance issues associated with this (as is also mentioned by others in comments or in other answers).

However, that being said, you can easily define your own noop function and, infact, many libraries and frameworks also provide noop functions. Below are some examples:

var noop = function () {};           // Define your own noop in ES3 or ES5
const noop = () => {};               // Define in ES6 as Lambda (arrow function)
setTimeout(noop, 10000);             // Using the predefined noop

setTimeout(function () {} , 10000);  // Using directly in ES3 or ES5
setTimeout(() => {} , 10000);        // Using directly in ES6 as Lambda (arrow function)

setTimeout(angular.noop, 10000);     // Using with AngularJS 1.x
setTimeout(jQuery.noop, 10000);      // Using with jQuery

Here is an alphabetical list of various implementations of noop functions (or related discussions or google searches):

AngularJS 1.x, Angular 2+ (Does not seem to have a native
implementation – use your own as shown above), Ember, jQuery, Lodash, NodeJS, Ramda, React (Does not seem to have a native implementation – use your own as shown above), RxJS,
Underscore

BOTTOM LINE: Although Function.prototype is an elegant way of expressing a noop in Javascript, however, there might be some performance issues related to its use. So, you can define and use your own (as shown above) or use one defined by the library/framework that you might be using in your code.