JavaScript Objects and Arrays

JavaScript objects are collections of properties and methods. JavaScript supports four kinds of objects:

  • Intrinsic objects, such as Array and String.

  • Objects that are created by yourself.

  • Host objects, like window and document.

  • ActiveX objects.

Learn more about JavaScript Objects

Expando Properties and Methods

In JavaScript all objects support expando properties and methods. These can be added and removed at run time. 

Example - Expando Properties and Methods

var x = newObject(); = "Fred";
x.age = 42;
x.getAge = function () {
    return this.age ;
document.write (;
document.write ( "<br/>" );
document.write ( x.age );
document.write ( "<br/>" );
document.write ( x.getAge ());
// Output: 
// Fred 
// 42 
// 42

When the property- or method name is not a simple identifier or is unknown at the time you write the script, an expression inside square brackets to index the property can be used.

var x = newObject();
// Add two expando properties that cannot be written in the
// syntax.
// The first contains invalid characters (spaces), so must be 
// written inside square brackets.
x [ "invalid identifier" ] = "This is the property value";
// The second expando name is a number, so it also must 
// be placed inside square brackets
x [ 100] = "100" ;

Arrays as Objects

In JavaScript, objects and arrays are handled almost identically, because arrays are merely a special kind of object. Both objects and arrays can have properties and methods.

JS JavaScript - Arrays as Objects

// An array with three elements
var x = newArray(3);
// Add some data
x [0] = "Hello";
x [1] = 42;
x [2] = new Date(2000, 1, 1);
document.write ( "original length is: " + x.length);
document.write ( "<br/>" );
// Add some expando properties 
x.expando = "JavaScript! "; 
x[ "another Expando" ] = "Windows";
// This will still display 3, since the two expando properties don't affect the length.
document.write ( "new length is : " + x.length);
// Output: 
// original length is: 3 
// new length is : 3 

In JavaScript, objects and arrays are handled almost identically, because arrays are merely a special kind of object. Both objects and arrays can have properties and methods.

JS JavaScript - Iterate and manipulate an array

var myText = "";
var numbers = [2, 5, 6, 77, 88];
    document.getElementById("demo").innerHTML = myText;
function myFunction(value, index, array) {
    myText = myText + value + "<br>";

Learn more about JavaScript Loop For Learn more about JavaScript Loop While

Multi-Dimensional Arrays

It's possible to get the behavior of multi-dimensional arrays in JavaScript by storing arrays within the elements of another array. 

JS JavaScript - Multi-Dimensional Arrays

// The size of the table.
var tableSize = 5;
// Loop counters. 
var i, j;
// Set the length of the array to tableSize + 1.  
// The first array index is zero, not 1. 
var resultTable = new Array(tableSize + 1);
// Loop for each major number (each row in the table)
for (i = 1; i <= tableSize; i++) {
// Create the columns in the table
    resultTable [i] = new Array(tableSize + 1);
// Fill the row with the results of the multiplication
for (j = 1; j <= tableSize; j++) {
        resultTable [i][j] = i * j;
document.write ( ResultTable [3][4]);
document.write ( "<br/>" );
document.write ( ResultTable [5][2]);
document.write ( "<br/>" );
document.write ( ResultTable [1][4]);
// Output: 
// 12 
// 10 
// 4

Learn more about JavaScript Array Sort Learn more about JavaScript Array Iteration

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JS JavaScript: Debugging

Searching for bugs and fixing them is called code debugging.

The bugs might be difficult to diagnose and therefore it is important to have a good approach to find and fix the bugs effectively.

JS JavaScript: Date Formats

There are generally 3 types of JavaScript date input formats:There are generally 3 types of JavaScript date input formats:

  • ISO Date
  • Date Short
  • ....

JS JavaScript: Switch

The switch statement evaluates an expression and match the expression's value to a case clause.

A switch statement can replace multiple if checks.
It gives a more descriptive way to compare a value with multiple variants.

JS JavaScript: Conditions

A condition is an expression that evaluates whether something is true or false. Conditions are very much used. Usually the code should execute one way if the condition is true and another way if the condition is false.


JavaScript is one of the 3 core language technologies of the World Wide Web that all web developers must learn:

1.      HTML to define the content of web pages.

2.      CSS to specify the layout of web pages.

3.      JavaScript to program the behavior of web pages.

JavaScript is a scripting or programming language that allows you to implement complex things on web pages. Every time a web page does more than just sit there and display static information for you to look at, displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. − you can bet that JavaScript is probably involved.

The benefits of using JavaScript are:

1.      You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.

2.      Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.

3.      Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.

4.      Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.


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