Programming & technology

An example to demonstrate how start interval & stop it using javascript.

var x = window.setInterval(
	function(greeting, name){
		var m = document.createElement("div");
                with(m.style){
                    height = "2px";
                    width = "50px";
                    position = "relative";
                    backgroundColor= "green";
                }
                document.body.appendChild(m);
	},
	1000,
	"hello",
	"world",
        document.body.onclick = function(){
	    clearInterval(x)
        }
);

Here’s how we create javascript object using Javascript Object Notation (JSON). After the code below is executed, it would show alert windows with text “Borey Lim”

//script to demonstrate creating object in javascript using JSON

var objectDemo = {
	firstName: "",
	lastName: "",
	displayName : function(){
		alert(this.firstName + " " + this.lastName);
	}
}

objectDemo.firstName = "Borey";
objectDemo.lastName = "Lim";
objectDemo.displayName();

Javascript provides flexible constructor. Below are sample code that implement the flexible constructor:

var Student = function(_department, _course, _year){
	department = _department || "";
	course = _course || "";
	year = _year || "";

	this.set_department = function(_department){
		department = _department;
	}

	this.set_course = function(_course){
		course = _course;
	}

	this.set_year = function(_year){
		year = _year;
	}

	this.display_information = function(){
		console.log("Information of the student:");
		console.log("Department: " + department);
		console.log("Course: " + course);
		console.log("Year: " + year);
	}
}

//constructor
var obj_student = new Student("Computer Information Scince", "ICT", "2");
obj_student.display_information();

var another_obj_student = new Student();
another_obj_student.set_department("Technology");
another_obj_student.set_course("BIS");
another_obj_student.set_year("Foundation");
another_obj_student.display_information();

Sample output:

Inheritance in javascript can be implemented easily using the concept of mixin. Below is an exmple to demonstrate javascript inheritance:

ClassA = function(){
	this.display = function(){
		console.log("here's a display function in ClassA");
	}

	this.str = function(){
		return "string in ClassA";
	}
}

ClassB = function(){
	ClassA.call(this);

//overriden method
	this.str = function(){
		return "string in ClassB";
        }
}

//instantiate object of ClassB
obj = new ClassB();

//calling display method from ClassA
obj.display();

//this will invoke str method in ClassB NOT in ClassA
console.log(obj.str());

As we are working with object or array, sometimes, we need to delete it’s property of element. Below is an example of a simple way to do it.

var display_before = function (str){
    return "before delete " + str;
}

var display_after = function (str){
    return "after delete " + str;
}

var obj = {x:12, y:15};
console.log(display_before("obj.x") + " " + obj.x);

//delete property x from object
delete obj.x;
console.log(display_after("obj.x") + " " + obj.x);

//delete array[2]
var array = [2, 4, 6, 8, 10]
console.log(display_before("array: ") + array);

array.splice(2,1);    //delete value 6 from array
console.log(display_after("index 2 from array: ") + array);

Sample result (in firebug plugin):