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Comment by CryoLogic | Hacker News Reader

Immediately invoked function expression - aka an anonymous function that executes as it is interpreted.

    (function() { console.log('test'); })();

In old versions of JavaScript, variables had to be scoped to the nearest function (rather than the nearest block) so IIFE where often used for namespacing:

    var $ = (function() { this.version = '1.2.3'; })();
    $.version; // 1.2.3

This worked because the function would be immediately invoked upon interpretation, scoping it's contents to itself (aliased by the variable name).

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Hate to be a wet blanket, but that second code sample won't work. The function doesn't return anything so $ === undefined. Even if it did, this in that context is bound to the global object, so is the same as setting a variable without var or let.

A proper example of IIFE for lexical scoping would be something like this:

     var numbers = "";
     (function(){
         for (var i=0; i<5; i++) {
             numbers += i + " ";
         }
     })();
     console.log(i) //undefined

Nowadays of course you could just use let instead of var

Your code snippet would kind of work as expected if used as a constructor. As in:

    var $ = function() { this.version = '1.2.3'; };
    var obj = new $;
    console.log(obj.version); //1.2.3

Of course that is not a IIFE.

Ah...brings me back to my SO days...

Hate to dry off the blanket but they just forgot the `new` keyword for `this` ;)

    var $ =  new (function() { this.version = '1.2.3'; })();
    console.log($.version); // '1.2.3'

EDIT: Or if you really want to abuse the spec

    var $ = (function() { if (!(this instanceof arguments.callee)) return new arguments.callee(); this.version = '1.2.3' })();
    console.log($.version); // '1.2.3'

lol. But yes, I do really want to abuse the spec. You could also do this:

    var $ = (function(){ this.version = '1.2.3'; return this; }).call({})
    console.log($.version); //1.2.3

But that's not quite as ugly so I guess I lose some points.

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