JavaScript - detect if *.js code is run under Browser or Node.js

In this short article, we would like to show how to check in a simple way if JavaScript source code is run under Browser or Node.js.

Quick solution: put the following code at the beginning of your program.

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"use strict"

​

const IS_NODE = typeof global === 'object' && '[object global]' === global.toString.call(global);

const IS_BROWSER = typeof window === 'object' && '[object Window]' === window.toString.call(window);

​

console.log(`IS_NODE: ${IS_NODE}`);

console.log(`IS_BROWSER: ${IS_BROWSER}`);

Node.js output:

Note: there are additional alternative ways how to do a more precise JavaScript environment detection, e.g. by checking other global objects: document, location, process, process.release.name, etc.

More precise detection could be useful when we do detection, not at the script beginning and global objects can be created in the code.