JavaScript Cookbook, 3rd Edition by John Paxton & Adam D. Scott & Shelley Powers

Author:John Paxton & Adam D. Scott & Shelley Powers [John Paxton]
Language: eng
Format: epub
Publisher: O'Reilly Media, Inc.
Published: 2020-11-24T16:00:00+00:00

Discussion

forEach() is an Array method, but the results of querySelectorAll() is a NodeList which is a different type of object than an Array. Thankfully, modern browsers have built in support for forEach, allowing us to iterate over a NodeList like an array.

Unfortunately, Internet Explorer (IE) does not support using forEach in this way. If you’d like to support IE, the recommended approach is to include a polyfill that uses a standard for loop under the hood:

if (window.NodeList && !NodeList.prototype.forEach) { NodeList.prototype.forEach = function(callback, thisArg) { thisArg = thisArg || window; for (var i = 0; i < this.length; i++) { callback.call(thisArg, this[i], i, this); } }; }

In the polyfill, we check for the existence of Nodelist.prototype.forEach. If it does not exist, a forEach method is added to the Nodelist prototype that uses a for loop to iterate over the results of a DOM query. By doing so, you can use the forEach syntax freely across your codebase.

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