Javascript "this" behavior notes

this.js

/*************
/ Call #1 Default Binding
**************/
function foo() {
    console.log( ": " + this.a );
}

// note var is dropped to make this global even when
// run with node.js that would otherwise cause the call
// site of foo to be called from within a module
// (function (exports, require, module, __filename, __dirname) { ... call site ...} )
a = 'a from global';

console.log('Call 1 (Default Binding): this points to global a');
foo(); // call site > 'default binding'
nl();

/*************
/ Call #2 Implicit Binding
**************/
var obj = {
    a: 'a from obj',
    foo: foo
};

console.log('Call 2 (Implicit Binding): this points to obj.a');
obj.foo(); // call site > 'implicit binding'
nl();


/*************
/ Call #3 Implicit Binding
**************/

// Note that only the last context of a function call
// establishes the call site
var obj2 = {
	a: 'a from obj2',
	obj: obj
};

console.log('Call 3 (Implicit Binding): last call site mean this points to obj.a, not obj2.a');
obj2.obj.foo(); // call site  > 'implicit binding'
nl();

/*************
/ Call #4 Implicit Binding Lost
**************/
// Watchout for implicit binding in wrapper functions
// this will happen in callbacks
function doFoo(fn) {
	fn(); // << this just became the call site
	// since there's no "a" in doFoo, this points to global a
}

var bar = obj.foo; // function reference / alias
console.log('Call 4 (Implicit Binding Lost): this points to global since bar is the call site');
bar(); // call site
nl();

/*************
/ Call #5 Implicit Binding Lost
**************/
// what happened with bar() above is what happens when you pass a function
console.log('Call 5 (Implicit Binding Lost): this points to global since doFoo is the call site');
doFoo(obj.foo);
nl();
// this means if doFoo is a callback, this will lose its context for this...

/*************
/ Call #6 Explicit / Hard Binding
**************/
console.log('Call 6 (Explicit / Hard Binding): this points to obj.a because it is hard bound with .call(...)');
console.log('bar.call(obj)');
bar.call(obj);
console.log('bar.call(obj2)');
bar.call(obj2);
nl();

/*************
/ Call #7 Explicit / Hard Binding
**************/
console.log('Call 7 (Hard Binding with built in bind): this points to obj.a becaus it is hard bound with .bind');
bar = foo.bind(obj);
bar();
nl();
// note, if bar took parameters, this would allow them... so, for example you could:
// 	bar = foo.bind(obj);
// 	bar(123);
// Assuming bar took parameters

 /*************
/ Call #8 New Binding
**************/
function newFoo(a) {
	this.a = a;
}

a = 4;

var bar = new newFoo(2);
console.log('Call 8 New Binding): this points  to the new newFoo');
console.log(bar.a);


// Binding Order
console.log('new binding');
console.log('explicit biding');
console.log('implicit binding');
console.log('default binding');



//////////
function nl() {
	console.log('');
}