In javascript detect the "Window" part of [object Window]

Question

In javascript detect the "Window" part of [object Window]

In javascript detect the "Window" part of [object Window] and/or tell if code is running on a node server or a browser

A litter more context. I'm writing a module for nodejs that is supposed to run on both the client and the server. I need to to differently in a couple places so I need to detect where it's running. right now I'm passing "this" to the init function which give me [object Object] on the server and [object Window] in browser. ... but I don't know how to check against the Window / Object part. typeof just seems to check the leading 'object' part. Thoughts? Thanks in advance

javascript
node.js

Answer 1

If you're sure you'll receive [object Object] in node.js and [object Window] in browser, then just check

var isBrowser = (this.toString().indexOf('Window') != -1);
var isServer = !isBrowser;

The indexOf method of a string checks for the position of its parameter in that string. Return value -1 means the parameter is not present as a substring.

Update

As others have suggested to just check for the existence of the window object, you can equivalently check for other objects that you expect to be present in a browser, like navigator or location. However, this kind of check, that has been suggested above:

var isBrowser = (this.window == this);

will end up with a reference error in node.js. The correct way to do this is

var isBrowser = ('window' in this);

or, as I noted

var isBrowser = ('navigator' in this);
var isBrowser = ('location' in this);

Answer 2

[object Window] is not reliable. Some older browsers just say [object] or [object Object] regardless of the type of object.

Try this instead:

var isBrowser = this instanceof Window;

Or, since I've never used Node.js, how about this?

var isBrowser = typeof Window != "undefined";

Answer 3

If you just want to know if you're running on Node, just see if this === this.window.

if (this === this.window) {
    // Browser
} else {
    // Node
}

This is more reliable than hoping that toString's implementation is consistent, which it isn't.

Answer 4

For simplicity, I don't think you can beat:

if('window' in this) {
    // It's a browser
}

Answer 5

Basically, you are asking how to detect Node.js in your script =x

The following was modified and extended from Underscore.js, which i use a varient for some of my client/server module code too. It basically scans for global variables that are somewhat unique to node.js (unless you created them in client side =x)

This is to provide an alternative answer, in case it was all that was needed.

(function() {
    //this is runned globally at the top somewhere
    //Scans the global variable space for variables unique to node.js
    if(typeof module !== 'undefined' && module.exports && typeof require !== 'undefined' && require.resolve ) {
        this.isNodeJs = true;
    } else {
        this.isNodeJs = false;
    }
})();

Alternatively, if you want to call it only when needed

function isNodeJs() {
    //this is placed globally at the top somewhere
    //Scans the global variable space for variables unique to node.js
    if(typeof module !== 'undefined' && module.exports && typeof require !== 'undefined' && require.resolve ) {
        return true;
    } else {
        return false;
    }
};