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();
x.name = "Fred";
x.age = 42;
 
x.getAge = function () {
    return this.age ;
};
 
document.write ( x.name);
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
// object.property 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];
 
numbers.forEach(myFunction);
    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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Check this out

JS JavaScript: Variables

A variable contains a value. When you use the variable, you refer to the data it represents. You use variables to store, retrieve and manipulate values in your code.

JS JavaScript: Switch

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

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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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