Javascript Function Definitions

Question

I was wondering why the Vector variable defined within this self executing javascript function doesn't require a var before it? Is this just some other type of syntax for creating a named function? Does this make it so we can't pass Vector as an argument to other functions?

(function() {
    Vector = function(x, y) {
        this.x = x;
        this.y = y;

        return this;
    };

   //...snip   
})()

Answer 1

Defining a variable without var makes it global.

Answer 2

The code construct above makes Vector a global variable in the namespace, which might be OK since it is probably intended to be used as constructor.

I would not recommend adding to the global name space, actually take a look at requirejs its a very nice way to work with modular JS.

Answer 3

Vector in this case will be attached to the current this which would be window. At least in the code you presented, there doesn't seem to be a need for the enclosing self executing function.

Answer 4

Defining Vector any other way would only create it within the scope of the closure; and would not be available outside the closure.

(function() {
    var Vector = function(x, y) {
        this.x = x;
        this.y = y;

        return this;
    };

    function Vector() {
        // blah
    };

   //...snip   
})()

var something = new Vector() // ERROR :<

Nothing "requires" the var keyword; using it defines the scope the variable is available within. Not using it means the variable is created in the global scope.