gistfile1.txt

/*
	ASSIGNMENT

	Implement a stack data structure as a JavaScript object that contains the following methods:

	push(data) - Adds a data element to the stack
	The parameter is the data element to add to the stack.

	pop(callback) - Removes a data element from the stack
	The parameter to pop is a callback function that should expect two parameters - err and value. The callback's first param, err, is set to null if the pop operation was successful or "Underflow" if the stack was empty when called. The callback's second parameter, value, is the value removed from the stack.

*/


var LinkedList = function() {
	this.head = null;
}

var newNode = function( data ) {
	this.data = data;
	this.prev = null;
}

LinkedList.prototype.push = function ( data ) {
	var node = new newNode ( data );

	node.prev = this.head || null;
	this.head = node;
}

LinkedList.prototype.pop = function () {
	if ( this.head === null && this.head.prev === undefined ) { return "nothing there" }
	this.head = this.head.prev;
}

// test out the application

var ll = new LinkedList();

// insert new 
ll.push ( '1. hi' );
ll.push ( '2. hi' );
ll.push ( '3. hi' );

console.log ( ll.head );

ll.pop ();
ll.pop ();

console.log ( ll.head );