Javascript: Scope

Javascript: Scope.js

/*In JavaScript, functions are the only things that create a new scope*/
var globalVar = "This is a global variable.";
var globalFunction = function() {
    var localVar = "This is a local variable.";

    var localFunction = function() {
        var localVar = "hello, world!";
        alert(localVar);
    };

    localFunction();
    alert(localVar);
};
globalFunction();

var g = "global";
function go() { 
    var l = "local";
}
go();
alert(l); // throws a reference error

//JavaScript uses the this keyword to get a reference to the current execution context.
function go() { console.debug(this); }
go(); //gives you a reference to the top-level execution context; in a browser, that’s the browser window itself.

var myObject = {    
    go: function() {
        console.debug(this);
    }   
};
myObject.go(); // console.debugs a reference to myObject

//when using functions as constructors, you see the same behavior:
function MyClass() {
    this.go = function() {
        console.debug(this);
    }
}

var instance1 = new MyClass();
var instance2 = new MyClass();

instance1.go(); // console.debugs a reference to the MyClass instance1
instance2.go(); // console.debugs a reference to the MyClass instance2

//JavaScript functions have two methods available to them that are of particular interest for handling context. Let’s look at call:

showCount.call(products, 4);

//Apply is very similar but is used when you don’t know how many arguments you will be passing. It takes an array as its second parameter:

showCount.apply(products, [4]);