Javascript global module or global variable

Question

I couldn't come up with a better question title, sorry.

My question is, in he.js as per https://github.com/mathiasbynens/he/blob/master/he.js , they are using the following code:

/*! https://mths.be/he v0.5.0 by @mathias | MIT license */
;(function(root) {

    //...omitted

    var he = {
        'version': '0.5.0',
        'encode': encode,
        'decode': decode,
        'escape': escape,
        'unescape': decode
    };

    // Some AMD build optimizers, like r.js, check for specific condition patterns
    // like the following:
    if (
        typeof define == 'function' &&
        typeof define.amd == 'object' &&
        define.amd
    ) {
        define(function() {
            return he;
        });
    }   else if (freeExports && !freeExports.nodeType) {
        if (freeModule) { // in Node.js or RingoJS v0.8.0+
            freeModule.exports = he;
        } else { // in Narwhal or RingoJS v0.7.0-
            for (var key in he) {
                has(he, key) && (freeExports[key] = he[key]);
            }
        }
    } else { // in Rhino or a web browser
        root.he = he;
    }

}(this));

And if you import this into your page as

<script src="he.js"></script>

You will be able to call the methods in your page as he.encode(...) .

My question is, how exactly does it set the variable he ?

I mean, I can see the

    } else { // in Rhino or a web browser
        root.he = he;
    }
}(this));

But at the call of }(this)); , what exactly is this ?

Answer 1

Let's simplify:

;(function(root) {
    ...
}(this));

So, we have a function that takes an argument called root . This function is being immediately invoked ( http://benalman.com/news/2010/11/immediately-invoked-function-expression/ ), and we are passing the value this to it.

In this context, this is your global object. If you are using a browser, your global object will be window .

So, if you are indeed using a browser:

 root.he = he;

is actually the same as:

window.he = he;

And note, we don't necessarily need to be using a browser, thanks to platforms like Node there are now other contexts where the this global object is something other than window . That's why the other doesn't specify window explicitly and goes through this particular exercise.