15 JavaScript Objects

Dr M. Vijayalakshmi

JavaScript Popup Boxes

Alert Box

An alert box is often used if we want to ensure information to the user. When an alert box pops up, the user will have to click “OK” to proceed.

Example:

alert(“Hello World!”)

</script>

Confirm Box

A confirm box is often used when you want the user to verify or accept something. When a confirm box pops up, the user will have to click either “OK” or “Cancel” to proceed. If the user clicks “OK”, the box returns true. If the user clicks “Cancel”, the box returns false.

Prompt Box

A prompt box is often used if you want the user to input a value before entering a page. When a prompt box pops up, the user will have to click either “OK” or “Cancel” to proceed after entering an input value. If the user clicks “OK“, the box returns the input value.If the user clicks “Cancel“, the box returns null.

Example:

alert(“This is an Alert method”);

JavaScript – Example

<html>

<body>

<p>Click the button to calculate x.</p>

<br/>Enter first number:

<input type=”text” id=”txt1″ name=”text1″>Enter second number:

function myFunction() {

var y = parseInt(document.getElementById(“txt1”).value);

var z = parseInt(document.getElementById(“txt2”).value);

var x = y + z;

document.getElementById(“demo”).innerHTML = x;

}

</script>

</body>

</html>

Output:

Using Arrays

An array is an ordered collection of values referenced by a single variable name. The syntax for creating an array variable is:

var variable = new Array(size);

where variable is the name of the array variable and size is the number of elements in the array (optional).

var variable = new Array(values);

where values are the array elements enclosed in quotes and separated by commas.

var Month=new Array(“”, “January”, “February”, “March”, “April”, “May”, “June ”, “July”, “August”, “September”, “October”, “November”, “December”);

To populate the array with values, use:

variable[i]=value;

JavaScript – Functions

We can define a function using the function keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block surrounded by curly braces.

Syntax:

<!–function functionname(parameter-list)

{

statements

}//–>

</script>

Example:

<!–

function sayHello()

{

alert(“Hello there”);

}

//–>

</script>

Example:

<html>

<head>

function sayHello()

{

document.write (“Hello there!”);

}

</script> </head>

<body>

<p>Click the followingbutton to call the function</p> <form>

<p> Use different text in write method and then try… <p> </form>

</body>

</html>

OUTPUT:

Function Parameters

It can take multiple parameters separated by comma.

Example:

<html>

<head>

function sayHello(name, age) {

document.write (name + ” is ” + age + ” years old.”); }

</script> </head>

<body>

<p>Click the following button to call the function</p> <form>

<p>Use different parameters inside the function and then try…</p>

</body>

</html>

OUTPUT

The return Statement

The Function can have an optional return statement. This statement should be the last statement in a function.

Example:

<html>

<head>

function concatenate(first, last)

{

var full;

full = first + last;

return full; }

function secondFunction()

{

var result;

result = concatenate(‘Zara’, ‘Ali’);

document.write (result );

} </script> </head> <body>

<p>Click the following button to call the function</p> <form>

<p>Use different parameters insi de the function and then try…</p> </body>

</html>

OUTPUT:

JavaScript – Objects

JavaScript is an Object Oriented Programming (OOP) Scripting language. It has the following features,

1. Encapsulation

2. Aggregation

3. Inheritance

4. Polymorphism

Object Properties:

Properties are the values associated with a JavaScript object.objectName.objectProperty = propertyValue;

example

var str = document.title;

Object Methods:

Methods are actions that can be performed on objects. Methods are stored in properties as function definitions.A function is a standalone unit of statements and a method is attached to an object and can be referenced by the this keyword.

document.write(“This is test”);

User-Defined Objects

Objects are variables too. But objects can contain many values.var car = {type:”Fiat”, model:”500″, color:”white”}; where values are written as name:value pairsMethods are stored in properties as function definitions.All user-defined objects and built-in objects are descendants of an object called Object.

The new Operator

The new operator is used to create an instance of an object. To create an object, the new operator is followed by the constructor method. The constructor methods are Object(), Array(), and Date(). These constructors are built-in JavaScript functions.

var employee = new Object();

var books = new Array(“C++”, “Perl”, “Java”);

var day = new Date(“August 15, 1947”);

The Object() Constructor

JavaScript has built-in constructors for native objects like,var x1 = new Object(); var x2 = new String(); var x3 = new Number(); var x4 = new Boolean() var x5 = new Array(); var x6 = new RegExp();

// A new Object object

// A new String object

// A new Number object

// A new Boolean object

// A new Array object

// A new RegExp object

var x7 = new Function(); // A new Function object var x8 = new Date(); // A new Date object.We can create an “object type” using an built-in constructor function.

Example :

<html>

<head>

<title>User-defined objects</title>

var book = new Object(); // Create the object book.subject = “JAVA”; // Assign properties to the object book.author = “Herbert Schildt”;

</script>

</head>

<body>

document.write(“Book name is : ” + book.subject + “<br>”); document.write(“Book author is : ” + book.author + “<br>”); </script>

</body>

</html>

OUTPUT:

Book name is : JAVA

Book author is : Herbert Schildt

Working with Object

We can create Object using a function (book) called as an object constructor. Once an object constructor is created, we can create new objects of the same type.

The example shows how we can create an “object type” using an object constructor function.

<html>

<head>

<title>User-defined objects</title>

function addPrice(amount)

{

this.price = amount;

}

function book(title, author)

{

this.title = title;

this.author = author;

this.addPrice = addPrice;

}

</script> </head>

<body>

var myBook = new book(“JAVA”, “Herbert Schildt”); myBook.addPrice(100);

document.write(“Book title is : ” + myBook.title + “<br>”);

document.write(“Book author is : ” + myBook.author + “<br>”);

document.write(“Book price is : ” + myBook.price + “<br>”);

</script>

</body>

</html>

OUTPUT:

Book title is : JAVA

Book author is : Herbert Schildt

Book price is : 100

The ‘with’ Keyword

The object specified as an argument ‘with’ becomes the default object for the duration of the block that follows. The properties and methods for the object can be used without naming the object.

Syntax :

with (object)

{

properties used without the object name and dot

}

Example:

<html>

<head>

<title>User-defined objects</title>

// Define a function which will work as a method function addPrice(amount){

with(this) { price = amount;

}

function book(title, author){ this.title = title;

this.author = author;

this.price = 0;

this.addPrice = addPrice; // Assign that method as property.

}

</script>

</head>

<body>

var myBook = new book(“JAVA”, “Herbert Schildt”); myBook.addPrice(100);

document.write(“Book title is : ” + myBook.title + “<br>”);

document.write(“Book author is : ” + myBook.author + “<br>”);

document.write(“Book price is : ” + myBook.price + “<br>”); </script>

</body>

</html>

OUTPUT:

Book title is : JAVA

Book author is : Herbert Schildt

Book price is : 100

JavaScript Native Objects

The following is the list of Built-in or Native objects. They are,

1. JavaScript Number Object

2. JavaScript Boolean Object

3. JavaScript String Object

4. JavaScript Array Object

5. JavaScript Date Object

6. JavaScript Math Object

7. JavaScript RegExp Object

1. JavaScript – The Number Object

The Number object represents numerical date, either integers or floating-point numbers.

Syntax:

var v1 = new Number(number);

Note: In the place of number, if you provide any non-number argument, then the argument cannot be converted into a number, it returns NaN (Not-a-Number).

Number Properties:

MAX_VALUE, MIN_VALUE, NaN, NEGATIVE_INFINITY, POSITIVE_INFINITY, prototype, constructor

Number Methods:

toExponential()

toFixed()

toLocaleString()

toPrecision()

toString()

valueOf()

2. JavaScript – The Boolean Object

The Boolean object represents two values, either “true” or “false”.

Syntax:

var v1 = new Boolean(value);

Boolean Properties

Constructor, prototype

Boolean Methods

toSource( )

toString( )

valueOf( )

3. JavaScript – The String Object

The String Object help us to work with strings.

Syntax:

var str = new String(string);

String Properties

constructor , length, prototype

String Methods

charAt(), charCodeAt(), concat(), indexOf(), lastIndexOf(), localeCompare(), match(), replace()

String Object – Example

<html >

<head>

<title>Character Processing Methods</title>

var s = “ZEBRA”;

var s2 = “AbCdEfG”;

document.writeln( “<p>Character at i ndex 0 in ‘” + s + “‘ is ” + s.charAt( 0 ) ); document.writeln( “<br />Character code at index 0 in ‘”+ s + “‘ is ” + s.charCodeAt( 0 ) + “</p>” );

document.writeln( “<p>'” + String.fromCharCode( 87, 79, 82, 68 ) + “‘ contains character codes 87, 79, 82 and 68</p>” )

document.writeln( “<p>'” + s2 + “‘ in lowercase is ‘” +s2.toLowerCase() + “‘” ); document.writeln( “<br />'” + s2 + “‘ in uppercase is ‘”+ s2.toUpperCase() + “‘</p>” );

</script>

</head><body></body></html>

4. JavaScript – The Arrays Object

The Array object lets you store multiple values in a single variable of same date type. The maximum length allowed for an array is 4,294,967,295.

Syntax:

var fruits = new Array( “apple”, “orange”, “mango” );

create array by simply assigning values

var fruits = [ “apple”, “orange”, “mango” ];

Accessing array elements

fruits[0] is the first element

fruits[1] is the second element

fruits[2] is the third element

Array Properties

Constructor, index, input, length, prototype

Array Methods

concat(), every(), filter(), forEach(), indexOf(), join(), lastIndexOf(), map(), pop(), push() , reduce(), reduceRight(), reverse(), shift(), slice(), some(), toSource(), sort(), s plice(), toString(), unshift()

Array Object – Example

<html >

<head>

<title>Initializing an Array with a Declaration</title> <script type = “text/javascript”>

function start()

{

var colors = new Array( “cyan”, “magenta”, “yellow”, “black” ); var integers1 = [ 2, 4, 6, 8 ];

var integers2 = [ 2, , , 8 ];

outputArray( “Array colors contains”, colors ); outputArray( “Array integers1 contains”, integers1 ); outputArray( “Array integers2 contains”, integers2 );

}

function outputArray( header, theArray )

{

document.writeln( “<h2>” + header + “</h2>” ); document.writeln( “<table border = \”1\”” +”width = \”100%\”>” ); document.writeln( “<thead><th width = \”100\” ” +”align = \”left\”>Subscript</th>” + “<th align = \”left\”>Value</th></thead><tbody>” );

for ( var i = 0; i < theArray.length; i++ )

document.writeln( “<tr><td>” + i + “</td><td>” + theArray[ i ] + “</td></tr>” ); document.writeln( “</tbody></table>” );

}

</script>

</head><body onload = “start()”><a href=index.html>back</a></body> </html>

5. JavaScript – The Date Object

Date objects are created with the new Date( ). Methods allow you to get and set the year, month, day, hour, minute, second, and millisecond fields of the object, using either local time or UTC (universal, or GMT) time.

Syntax:

new Date( )

new Date(milliseconds)

new Date(date string)

new Date(year,month,date [,hour, minute, second, millisecond ])

Date Properties:

constructor, prototype

Date Methods:

Date(), getDate(), getDay(), getFullYear(), getHours(), getMilliseconds(), getMinutes(), getMonth(), getSeconds(), getTime(), getTimezoneOffset(), getUTCDate(), setMinutes(), setMonth(), setSeconds(), setTime()

6. JavaScript – The Math Object

Unlike other global objects, Math is not a constructor. All the properties and methods of Math are static and can be called by using Math as an object without creating it. Syntax

var pi_val = Math.PI;

var sine_val = Math.sin(30);

Math Properties:

E \, LN2, LN10, LOG2E, LOG10E, PI, SQRT1_2, SQRT2

Math Methods:

abs(), acos() , asin(), atan() , atan2() , ceil(), cos(), exp(), floor(), log(), max(), min(), pow(), sin(), random(), round(), sqrt(), tan().

Math Object – Example

<html >

<head>

<title>Finding the Maximum of Three Values</title> <script type = “text/javascript”>

var input1 =

window.prom pt( “Enter first number”, “0” );

var input2 =

window.prom pt( “Enter second number”, “0” );

var input3 =window.prom

pt( “Enter third number”, “0” );

var value1 = parseFloat( input1 );

var value2 = parseFloat( input2 );

var value3 = parseFloat( input3 );

var maxValue = maximum( value1, value2, value3 );

document.writeln( “First number: ” + value1 +”<br />Second num ber: ” + value2

\”<br />Third num ber: ” + value3 +”<br />Maximum is: ” + maxValue ); function maximum( x, y, z ){

return Math.max( x, Math.max( y, z ) );

}

</script>

</head>

<body>

<p>Click Refresh (or Reload) to run the script again</p> <a href=index.html>back</a> </body>

</html>

OUTPUT:

Summary

This module explains about JavaScript Dialog boxes with examples. This module also gives an idea about arrays, functions and objects. Moreover, the module also discusses about Objects that are of two types called native/built-in objects and user defined objects.

Web Links

www.w3schools.com
http://www.tutorialspoint.com/javascript