How to check whether a script is running under Nod

Question

I have a script I am requiring from a Node.js script, which I want to keep JavaScript engine independent.

For example, I want to do exports.x = y; only if it’s running under Node.js. How can I perform this test?

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When posting this question, I didn’t know the Node.js modules feature is based on CommonJS.

For the specific example I gave, a more accurate question would’ve been:

How can a script tell whether it has been required as a CommonJS module?

Answer 1

const isNode =
  typeof process !== 'undefined' &&
  process.versions != null &&
  process.versions.node != null;

Answer 2

I currently stumbled over a wrong detection of Node which is not aware of the Node-environment in Electron due to a misleading feature-detection. The following solutions identify the process-environment explicitly.

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Identify Node.js only

(typeof process !== 'undefined') && (process.release.name === 'node')

This will discover if you're running in a Node-process, since process.release contains the "metadata related to the current [Node-]release".

After the spawn of io.js the value of process.release.name may also become io.js (see the process-doc). To proper detect a Node-ready environment i guess you should check as follows:

Identify Node (>= 3.0.0) or io.js

(typeof process !== 'undefined') &&
(process.release.name.search(/node|io.js/) !== -1)

This statement was tested with Node 5.5.0, Electron 0.36.9 (with Node 5.1.1) and Chrome 48.0.2564.116.

Identify Node (>= 0.10.0) or io.js

(typeof process !== 'undefined') &&
(typeof process.versions.node !== 'undefined')

@daluege's comment inspired me to think about a more general proof. This should working from Node.js >= 0.10. I didn't find a unique identifier for prior versions.

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P.s.: I am posting that answer here since the question lead me here, although the OP was searching for an answer to a different question.

Answer 3

Here's a pretty cool way to do it as well:

const isBrowser = this.window === this;

This works because in browsers the global 'this' variable has a self reference called 'window'. This self reference is not existent in Node.

• In the browser 'this' is a reference to the global object, called 'window'.
• In Node 'this' is a reference to the module.exports object.
  • 'this' is not a reference to the Node global object, called 'global'.
  • 'this' is not a reference to the the module variable declaration space.

To break the above suggested browser check you would have to do something like the following

this.window = this;

before executing the check.

Answer 4

Edit: Regarding your updated question: "How can a script tell whether it has been required as a commonjs module?" I don't think it can. You can check whether exports is an object (if (typeof exports === "object")), since the spec requires that it be provided to modules, but all that tells you is that ... exports is an object. :-)

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Original answer:

I'm sure there's some NodeJS-specific symbol (EventEmitter, perhaps no, you have to use require to get the events module; see below) that you could check for, but as David said, ideally you're better off detecting the feature (rather than environment) if it makes any sense to do so.

Update: Perhaps something like:

if (typeof require === "function"
    && typeof Buffer === "function"
    && typeof Buffer.byteLength === "function"
    && typeof Buffer.prototype !== "undefined"
    && typeof Buffer.prototype.write === "function") {

But that just tells you that you're in an environment with require and something very, very much like NodeJS's Buffer. :-)

Answer 5

The following works in the browser unless intentionally,explicitly sabotaged:

if(typeof process === 'object' && process + '' === '[object process]'){
    // is node
}
else{
    // not node
}

Bam.

Answer 6

I'm using process to check for node.js like so

if (typeof(process) !== 'undefined' && process.version === 'v0.9.9') {
  console.log('You are running Node.js');
} else {
  // check for browser
}

or

if (typeof(process) !== 'undefined' && process.title === 'node') {
  console.log('You are running Node.js');
} else {
  // check for browser
}

Documented here