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 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.