JavaScript Objects Introduction

JavaScript is an Object Oriented Programming (OOP) language.

An OOP language allows you to define your own objects and make your own variable types.

Object Oriented Programming

JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define your own objects and make your own variable types.
However, creating your own objects will be explained later, in the Advanced JavaScript section. We will start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each built-in JavaScript object in detail.
Note that an object is just a special kind of data. An object has properties and methods.

Properties

Properties are the values associated with an object.
In the following example we are using the length property of the String object to return the number of characters in a string:

The output of the code above will be:

Methods

Methods are the actions that can be performed on objects.
In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters:

The output of the code above will be:

HELLO SHIBASHISH!

How to style strings.

<html>
<body>

<script type="text/javascript">

    var txt = "Hello Shibashish!";

    document.write("<p>Big: " + txt.big() + "</p>");
    document.write("<p>Small: " + txt.small() + "</p>");

    document.write("<p>Bold: " + txt.bold() + "</p>");
    document.write("<p>Italic: " + txt.italics() + "</p>");

    document.write("<p>Fixed: " + txt.fixed() + "</p>");
    document.write("<p>Strike: " + txt.strike() + "</p>");

    document.write("<p>Fontcolor: " + txt.fontcolor("green") + "</p>");
    document.write("<p>Fontsize: " + txt.fontsize(6) + "</p>");

    document.write("<p>Subscript: " + txt.sub() + "</p>");
    document.write("<p>Superscript: " + txt.sup() + "</p>");

    document.write("<p>Link: " + txt.link("http://shibashishdotnetocean.blogspot.com/2011/12/javascript-objects.html") + "</p>");

    document.write("<p>Blink: " + txt.blink() + " (does not work in IE, Chrome, or Safari)</p>");

</script>

</body>
</html>
How to convert a string to lowercase or uppercase letters.
<html>
<body>

<script type="text/javascript">

var txt="Hello Shibashish!";
document.write(txt.toLowerCase() + "<br />");
document.write(txt.toUpperCase());

</script>

</body>
</html>

How to search for a specified value within a string.

<html>
<body>

<script type="text/javascript">
var str="Hello shibashish!";
document.write(str.match("shibashish") + "<br />");
document.write(str.match("shibushish") + "<br />");
document.write(str.match("shbashish") + "<br />");
document.write(str.match("shibashish!"));
</script>

</body>
</html>

How to replace a specified value with another value in a string.

<html>
<body>

<script type="text/javascript">

var str="Visit shibashish!";
document.write(str.replace("Visit","Lovely Boy"));

</script>
</body>
</html>

How to return the position of the first found occurrence of a specified value in a string.

<html>
<body>

<script type="text/javascript">
    var str = "Hello Shibashish!";
    document.write(str.indexOf("o") + "<br />");
    document.write(str.indexOf("Shibuna") + "<br />");
    document.write(str.indexOf("Shibashish"));
</script>

</body>
</html>

JavaScript Date Object

How to use the Date() method to get today's date.

<html>
<body>

<script type="text/javascript">

var d=new Date();
document.write(d);

</script>

</body>
</html>

Use getFullYear() to get the year.

<html>
<body>

<script type="text/javascript">

var d=new Date();
document.write(d.getFullYear());

</script>

</body>
</html>

getTime() returns the number of milliseconds since 01.01.1970

<html>
<body>

<script type="text/javascript">
var d=new Date();
document.write(d.getTime() + " milliseconds since 1970/01/01");
</script>

</body>
</html>

How to use setFullYear() to set a specific date.

<html>
<body>

<script type="text/javascript">

    var d = new Date();
    d.setFullYear(2011, 10, 3);
    document.write(d);

</script>

</body>
</html>

How to use toUTCString() to convert today's date (according to UTC) to a string.

<html>
<body>

<script type="text/javascript">

    var d = new Date();
    document.write("Original form: ");
    document.write(d + "<br />");
    document.write("To string (universal time): ");
    document.write(d.toUTCString());

</script>

</body>
</html>

Use getDay() and an array to write a weekday, and not just a number.

<html>
<body>

<script type="text/javascript">

var d=new Date();
var weekday=new Array(7);
weekday[0]="Sunday";
weekday[1]="Monday";
weekday[2]="Tuesday";
weekday[3]="Wednesday";
weekday[4]="Thursday";
weekday[5]="Friday";
weekday[6]="Saturday";

document.write("Today is " + weekday[d.getDay()]);

</script>

</body>
</html>

How to display a clock on your web page.

<html>
<head>
<script type="text/javascript">
function startTime()
{
var today=new Date();
var h=today.getHours();
var m=today.getMinutes();
var s=today.getSeconds();
// add a zero in front of numbers<10
m=checkTime(m);
s=checkTime(s);
document.getElementById('txt').innerHTML=h+":"+m+":"+s;
t=setTimeout('startTime()',500);
}

function checkTime(i)
{
if (i<10)
{
i="0" + i;
}
return i;
}
</script>
</head>

<body onload="startTime()">
<div id="txt"></div>
</body>
</html>

Create a Date Object

The Date object is used to work with dates and times.
Date objects are created with the Date() constructor.
There are four ways of instantiating a date:

new Date() // current date and time
new Date(milliseconds) //milliseconds since 1970/01/01
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)

Most parameters above are optional. Not specifying, causes 0 to be passed in.
Once a Date object is created, a number of methods allow you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and milliseconds of the object, using either local time or UTC (universal, or GMT) time.
All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds.
Some examples of instantiating a date:

var today = new Date()
var d1 = new Date("October 13, 1975 11:13:00")
var d2 = new Date(79,5,24)
var d3 = new Date(79,5,24,11,33,0)

Set Dates

We can easily manipulate the date by using the methods available for the Date object.
In the example below we set a Date object to a specific date (14th January 2010):

var myDate=new Date();
myDate.setFullYear(2010,0,14);

And in the following example we set a Date object to be 5 days into the future:

var myDate=new Date();
myDate.setDate(myDate.getDate()+5);

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself!

Compare Two Dates

The Date object is also used to compare two dates.
The following example compares today's date with the 14th January 2100:

var x=new Date();
x.setFullYear(2100,0,14);
var today = new Date();

if (x>today)
{
alert("Today is before 14th January 2100");
}
else
{
alert("Today is after 14th January 2100");
}

JavaScript Array Object

simple Ex:

<html>
<body>

<script type="text/javascript">
var i;
var mynames = new Array();
mynames [0] = "shibashish";
mynames [1] = "mohanty";
mynames [2] = "Aul";
//foreach(i in mynames)
for (i=0;i<mynames .length;i++)
{
document.write(mynames [i] + "<br />");
}
</script>

</body>
</html>

What is an Array?

An array is a special variable, which can hold more than one value, at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

var car1="Saab";
var car2="Volvo";
var car3="BMW";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The best solution here is to use an array!
An array can hold all your variable values under a single name. And you can access the values by referring to the array name.
Each element in the array has its own ID so that it can be easily accessed.

Create an Array

An array can be defined in three ways.
The following code creates an Array object called myCars:
1:

var myCars=new Array(); // regular array (add an optional integer
myCars[0]="Saab"; // argument to control array's size)
myCars[1]="Volvo";
myCars[2]="BMW";

var myCars=new Array("Saab","Volvo","BMW"); // condensed array

var myCars=["Saab","Volvo","BMW"]; // literal array

Note: If you specify numbers or true/false values inside the array then the variable type will be Number or Boolean, instead of String.

Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.
The following code line:

document.write(myCars[0]);

will result in the following output:

Saab

Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

myCars[0]="Opel";

Now, the following code line:

document.write(myCars[0]);

will result in the following output:

Opel

join two arrays-concat():

<html>
<body>

<script type="text/javascript">

var parents = ["jagannath", "baidyannath"];
var children = ["Raja", "shibuna"];
var family = parents.concat(children);
document.write(family);

</script>

</body>
</html>

join three arrays-concat():

<html>
<body>

<script type="text/javascript">

var parents = ["jagannath", "baidyannath"];
var sisters= ["madhu", "sonali", "barsha"];
var children = ["Raja", "shibuna"];
var family = parents.concat(sisters, children);
document.write(family);

</script>

</body>
</html>

join all elements of an array into a string-join():

Remove the last element of an array-pop():

<html>
<body>

<script type="text/javascript">

var family= ["shibashish", "debashish", "madhu", "sonali"];
document.write(family.pop() + "<br />");
document.write(family+ "<br />");
document.write(family.pop() + "<br />");
document.write(family);

</script>

</body>
</html>

Add new item to the end of an array-push():

<html>
<body>

<script type="text/javascript">
    var family = ["shibashish", "debashish", "madhu", "sonali"];
    document.write(family.push("barsha") + "<br />");
    document.write(family + "<br />");
    document.write(family.push("shibuna","raja") + "<br />");
    document.write(family);


</script>

</body>
</html>

Reverse the order of the element-reverse():

<html>
<body>

<script type="text/javascript">

var family = ["shibashish", "debashish", "madhu", "sonali"];
document.write(family .reverse());

</script>

</body>
</html>

Remove the first element of an array-shift():

<html>
<body>

<script type="text/javascript">

var family= ["shibashish", "debashish", "madhu", "sonali"];
document.write(family.shift() + "<br />");
document.write(family+ "<br />");
document.write(family.shift() + "<br />");
document.write(family);

</script>

</body>
</html>

Select elements from an array-slice():

<html>
<body>

<script type="text/javascript">
    var family = ["shibashish", "debashish", "madhu", "sonali"];
    document.write(family.slice(0, 1) + "<br />");
    document.write(family.slice(2) + "<br />");
    document.write(family.slice(-3) + "<br />");
    document.write(family);


</script>
</body>
</html>

Sort an array (alphabetically and ascending)-sort():

<html>
<body>

<script type="text/javascript">

var family = ["shibashish", "debashish", "madhu", "sonali"];
document.write(family .sort());

</script>

</body>
</html>

Sort numbers (numerically and ascending)-sort():

<html>
<body>

<script type="text/javascript">

    function sortNumber(a, b) {
        return a - b;
    }

    var n = ["10", "5", "40", "25", "100", "1"];
    document.write(n.sort(sortNumber));

</script>

</body>
</html>

Sort numbers (numerically and descending)-sort():

<html>
<body>

<script type="text/javascript">

    function sortNumber(a, b) {
        return b - a;
    }

    var n = ["10", "5", "40", "25", "100", "1"];
    document.write(n.sort(sortNumber));

</script>

</body>
</html>

Add an element to position 2 in an array -splice():

<html>
<body>

<script type="text/javascript">

    var family = ["shibashish", "debashish", "madhu", "sonali"];
    document.write("Added: " + family.splice(2, 0, "lala") + "<br />");
    //check the below comment line for better understand
    //document.write("Added: " + family.splice(2, 2, "lala") + "<br />");
    //document.write("Added: " + family.splice(2, 1, "lala") + "<br />");
    document.write(family);

</script>

</body>
</html>

Convert an array to a string-toString():

<html>
<body>

<script type="text/javascript">

var family = ["shibashish", "debashish", "madhu", "sonali"];
document.write(family .toString());

</script>

</body>
</html>

Add new element to the beginning of an array -unshift():

<html>
<body>

<script type="text/javascript">

    var family = ["shibashish", "debashish", "madhu", "sonali"];
    document.write(family + "<br />");
    document.write(family.unshift("lala") + "<br />");
    document.write(family + "<br />");
    document.write(family.unshift("raja", "shibuna") + "<br />");
    document.write(family);

</script>

</body>
</html>

JavaScript Boolean Object

Check if a Boolean object is true or false.

<html>
<body>

<script type="text/javascript">
var b1=new Boolean( 0);
var b2=new Boolean(1);
var b3=new Boolean("");
var b4=new Boolean(null);
var b5=new Boolean(NaN);
var b6=new Boolean("false");

document.write("0 is boolean "+ b1 +"<br />");
document.write("1 is boolean "+ b2 +"<br />");
document.write("An empty string is boolean "+ b3 + "<br />");
document.write("null is boolean "+ b4+ "<br />");
document.write("NaN is boolean "+ b5 +"<br />");
document.write("The string 'false' is boolean "+ b6 +"<br />");
</script>

</body>
</html>

Create a Boolean Object

The Boolean object represents two values: "true" or "false".
The following code creates a Boolean object called myBoolean:

var myBoolean=new Boolean();

If the Boolean object has no initial value, or if the passed value is one of the following:

0
-0
null
""
false
undefined
NaN

the object it is set to false. For any other value it is set to true (even with the string "false")!

JavaScript Math Object

How to use round().

<html>
<body>

<script type="text/javascript">

document.write(Math.round(0.60) + "<br />");
document.write(Math.round(0.50) + "<br />");
document.write(Math.round(0.49) + "<br />");
document.write(Math.round(-4.40) + "<br />");
document.write(Math.round(-4.60));

</script>

</body>
</html>

How to use random() to return a random number between 0 and 1.

<html>
<body>

<script type="text/javascript">

//return a random number between 0 and 1
document.write(Math.random() + "<br />");

//return a random integer between 0 and 10
document.write(Math.floor(Math.random()*11));

</script>

</body>
</html>

How to use max() to return the number with the highest value of two specified numbers.

<html>
<body>

<script type="text/javascript">
document.write(Math.max(5,10) + "<br />");
document.write(Math.max(0,150,30,20,38) + "<br />");
document.write(Math.max(-5,10) + "<br />");
document.write(Math.max(-5,-10) + "<br />");
document.write(Math.max(1.5,2.5));
</script>

</body>
</html>

How to use min() to return the number with the lowest value of two specified numbers.

<html>
<body>

<script type="text/javascript">

document.write(Math.min(5,10) + "<br />");
document.write(Math.min(0,150,30,20,38) + "<br />");
document.write(Math.min(-5,10) + "<br />");
document.write(Math.min(-5,-10) + "<br />");
document.write(Math.min(1.5,2.5));

</script>

</body>
</html>

Math Object

The Math object allows you to perform mathematical tasks.
The Math object includes several mathematical constants and methods.
Syntax for using properties/methods of Math:

var x=Math.PI;
var y=Math.sqrt(16);

Note: Math is not a constructor. All properties and methods of Math can be called by using Math as an object without creating it.

Mathematical Constants

JavaScript provides eight mathematical constants that can be accessed from the Math object. These are: E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E.
You may reference these constants from your JavaScript like this:

Math.E
Math.PI
Math.SQRT2
Math.SQRT1_2
Math.LN2
Math.LN10
Math.LOG2E
Math.LOG10E

Mathematical Methods

In addition to the mathematical constants that can be accessed from the Math object there are also several methods available.
The following example uses the round() method of the Math object to round a number to the nearest integer:

document.write(Math.round(4.7));

The code above will result in the following output:

The following example uses the random() method of the Math object to return a random number between 0 and 1:

document.write(Math.random());

The code above can result in the following output:

0.27015238226521243

The following example uses the floor() and random() methods of the Math object to return a random number between 0 and 10:

document.write(Math.floor(Math.random()*11));

The code above can result in the following output:

JavaScript RegExp Object

What is RegExp?

A regular expression is an object that describes a pattern of characters.
When you search in a text, you can use a pattern to describe what you are searching for.
A simple pattern can be one single character.
A more complicated pattern can consist of more characters, and can be used for parsing, format checking, substitution and more.
Regular expressions are used to perform powerful pattern-matching and "search-and-replace" functions on text.

Syntax

var patt=new RegExp(pattern,modifiers);

or more simply:

var patt=/pattern/modifiers;

pattern specifies the pattern of an expression
modifiers specify if a search should be global, case-sensitive, etc.

RegExp Modifiers

Modifiers are used to perform case-insensitive and global searches.
The i modifier is used to perform case-insensitive matching.
The g modifier is used to perform a global match (find all matches rather than stopping after the first match).

Example 1

<html>
<body>

<script type="text/javascript">
var str = "Visit shibashish";
var patt1 = /shibashish/i;
document.write(str.match(patt1));
</script>

</body>
</html>

Do a case-insensitive search for "w3schools" in a string:

var str="Visit shibashish";
var patt1=/shibashish/i;

The marked text below shows where the expression gets a match:

Visit shibashish

Example 2

<html>
<body>

<script type="text/javascript">

var str="Is this all there is?";
var patt1=/is/g;
document.write(str.match(patt1));

</script>

</body>
</html>
Do a global search for "is":

var str="Is this all there is?";
var patt1=/is/g;

The marked text below shows where the expression gets a match:

Is this all there is?

Example 3

<html>
<body>

<script type="text/javascript">

var str="Is this all there is?";
var patt1=/is/gi;
document.write(str.match(patt1));

</script>

</body>
</html>

Do a global, case-insensitive search for "is":

var str="Is this all there is?";
var patt1=/is/gi;

The marked text below shows where the expression gets a match:

Is this all there is?

test()

The test() method searches a string for a specified value, and returns true or false, depending on the result.
The following example searches a string for the character "e":

Example

<html>
<body>

<script type="text/javascript">
var patt1=new RegExp("e");

document.write(patt1.test("The best things in life are free"));
</script>

</body>
</html>

var patt1=new RegExp("e");
document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

true

exec()

The exec() method searches a string for a specified value, and returns the text of the found value. If no match is found, it returns null.
The following example searches a string for the character "e":

Example 1

<html>
<body>

<script type="text/javascript">
var patt1=new RegExp("e");

document.write(patt1.exec("The best things in life are free"));
</script>

</body>
</html>

var patt1=new RegExp("e");
document.write(patt1.exec("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

JavaScript Browser Detection

The Navigator object contains information about the visitor's browser.

Browser Detection

Almost everything in this tutorial works on all JavaScript-enabled browsers. However, there are some things that just don't work on certain browsers - especially on older browsers.
Sometimes it can be useful to detect the visitor's browser, and then serve the appropriate information.
The Navigator object contains information about the visitor's browser name, version, and more.
Note

Note: There is no public standard that applies to the navigator object, but all major browsers support it.

The Navigator Object

The Navigator object contains all information about the visitor's browser:

Example

<div id="example"></div>

<script type="text/javascript">

txt = "<p>Browser CodeName: " + navigator.appCodeName + "</p>";
txt+= "<p>Browser Name: " + navigator.appName + "</p>";
txt+= "<p>Browser Version: " + navigator.appVersion + "</p>";
txt+= "<p>Cookies Enabled: " + navigator.cookieEnabled + "</p>";
txt+= "<p>Platform: " + navigator.platform + "</p>";
txt+= "<p>User-agent header: " + navigator.userAgent + "</p>";

document.getElementById("example").innerHTML=txt;

</script>

Try it yourself »

JavaScript Cookies

A cookie is often used to identify a user.

What is a Cookie?

A cookie is a variable that is stored on the visitor's computer. Each time the same computer requests a page with a browser, it will send the cookie too. With JavaScript, you can both create and retrieve cookie values.
Examples of cookies:

Name cookie - The first time a visitor arrives to your web page, he or she must fill in her/his name. The name is then stored in a cookie. Next time the visitor arrives at your page, he or she could get a welcome message like "Welcome John Doe!" The name is retrieved from the stored cookie
Password cookie - The first time a visitor arrives to your web page, he or she must fill in a password. The password is then stored in a cookie. Next time the visitor arrives at your page, the password is retrieved from the cookie
Date cookie - The first time a visitor arrives to your web page, the current date is stored in a cookie. Next time the visitor arrives at your page, he or she could get a message like "Your last visit was on Tuesday August 11, 2005!" The date is retrieved from the stored cookie

Create and Store a Cookie

In this example we will create a cookie that stores the name of a visitor. The first time a visitor arrives to the web page, he or she will be asked to fill in her/his name. The name is then stored in a cookie. The next time the visitor arrives at the same page, he or she will get welcome message.
First, we create a function that stores the name of the visitor in a cookie variable:

function setCookie(c_name,value,exdays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate() + exdays);
var c_value=escape(value) + ((exdays==null) ? "" : "; expires="+exdate.toUTCString());
document.cookie=c_name + "=" + c_value;
}

The parameters of the function above hold the name of the cookie, the value of the cookie, and the number of days until the cookie expires.
In the function above we first convert the number of days to a valid date, then we add the number of days until the cookie should expire. After that we store the cookie name, cookie value and the expiration date in the document.cookie object.
Then, we create another function that returns a specified cookie:

The function above makes an array to retrieve cookie names and values, then it checks if the specified cookie exists, and returns the cookie value.
Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not set it will display a prompt box, asking for the name of the user, and stores the username cookie for 365 days, by calling the setCookie function:

All together now:

Example

<html>
<head>
<script type="text/javascript">
function getCookie(c_name)
{
var i,x,y,ARRcookies=document.cookie.split(";");
for (i=0;i<ARRcookies.length;i++)
{
x=ARRcookies[i].substr(0,ARRcookies[i].indexOf("="));
y=ARRcookies[i].substr(ARRcookies[i].indexOf("=")+1);
x=x.replace(/^\s+|\s+$/g,"");
if (x==c_name)
    {
    return unescape(y);
    }
}
}

function setCookie(c_name,value,exdays)
{
var exdate=new Date();
exdate.setDate(exdate.getDate() + exdays);
var c_value=escape(value) + ((exdays==null) ? "" : "; expires="+exdate.toUTCString());
document.cookie=c_name + "=" + c_value;
}

function checkCookie()
{
var username=getCookie("username");
if (username!=null && username!="")
{
alert("Welcome again " + username);
}
else
{
username=prompt("Please enter your name:","");
if (username!=null && username!="")
    {
    setCookie("username",username,365);
    }
}
}
</script>
</head>
<body onload="checkCookie()">
</body>
</html>

Try it yourself »

JavaScript Form Validation

JavaScript can be used to validate data in HTML forms before sending off the content to a server.
Form data that typically are checked by a JavaScript could be:

has the user left required fields empty?
has the user entered a valid e-mail address?
has the user entered a valid date?
has the user entered text in a numeric field?

Required Fields

The function below checks if a field has been left empty. If the field is blank, an alert box alerts a message, the function returns false, and the form will not be submitted:

function validateForm()
{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
{
alert("First name must be filled out");
return false;
}
}

The function above could be called when a form is submitted:

Example

<form name="myForm" action="demo_form.asp" onsubmit="return validateForm()" method="post">
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>

Try it yourself »

E-mail Validation

The function below checks if the content has the general syntax of an email.
This means that the input data must contain an @ sign and at least one dot (.). Also, the @ must not be the first character of the email address, and the last dot must be present after the @ sign, and minimum 2 characters before the end:

function validateForm()
{
var x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var dotpos=x.lastIndexOf(".");
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length)
{
alert("Not a valid e-mail address");
return false;
}
}

The function above could be called when a form is submitted:

Example

<form name="myForm" action="demo_form.asp" onsubmit="return validateForm();" method="post">
Email: <input type="text" name="email">
<input type="submit" value="Submit">
</form>

Try it yourself »

JavaScript Timing Events

With JavaScript, it is possible to execute some code after a specified time-interval. This is called timing events.
It's very easy to time events in JavaScript. The two key methods that are used are:

setTimeout() - executes a code some time in the future
clearTimeout() - cancels the setTimeout()

Note: The setTimeout() and clearTimeout() are both methods of the HTML DOM Window object.

The setTimeout() Method

Syntax

var t=setTimeout("javascript statement",milliseconds);

The setTimeout() method returns a value. In the syntax defined above, the value is stored in a variable called t. If you want to cancel the setTimeout() function, you can refer to it using the variable name.
The first parameter of setTimeout() can be a string of executable code, or a call to a function.
The second parameter indicates how many milliseconds from now you want to execute the first parameter.
Note: There are 1000 milliseconds in one second.

Example

When the button is clicked in the example below, an alert box will be displayed after 3 seconds.

Example

<html>
<head>
<script type="text/javascript">
function timeMsg()
{
var t=setTimeout("alertMsg()",3000);
}
function alertMsg()
{
alert("Hello");
}
</script>
</head>

<body>
<form>
<input type="button" value="Display alert box in 3 seconds"
onclick="timeMsg()" />
</form>
</body>
</html>

Try it yourself »

Example - Infinite Loop

To get a timer to work in an infinite loop, we must write a function that calls itself.
In the example below, when a button is clicked, the input field will start to count (for ever), starting at 0.
Notice that we also have a function that checks if the timer is already running, to avoid creating additional timers, if the button is pressed more than once:

Example

<html>
<head>
<script type="text/javascript">
var c=0;
var t;
var timer_is_on=0;

function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}

function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}
</script>
</head>

<body>
<form>
<input type="button" value="Start count!" onclick="doTimer()">
<input type="text" id="txt" />
</form>
</body>
</html>

Try it yourself »

The clearTimeout() Method

Syntax

clearTimeout(setTimeout_variable)

Example

The example below is the same as the "Infinite Loop" example above. The only difference is that we have now added a "Stop Count!" button that stops the timer:

Example

<html>
<head>
<script type="text/javascript">
var c=0;
var t;
var timer_is_on=0;

function timedCount()
{
document.getElementById('txt').value=c;
c=c+1;
t=setTimeout("timedCount()",1000);
}

function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}

function stopCount()
{
clearTimeout(t);
timer_is_on=0;
}
</script>
</head>

<body>
<form>
<input type="button" value="Start count!" onclick="doTimer()">
<input type="text" id="txt">
<input type="button" value="Stop count!" onclick="stopCount()">
</form>
</body>
</html>

Try it yourself »

More Examples

Another simple timing
A clock created with a timing event

JavaScript Create Your Own Objects

Objects are useful to organize information.

Try it Yourself - Examples

Create a direct instance of an object
Create a template for an object

JavaScript Objects

Earlier in this tutorial we have seen that JavaScript has several built-in objects, like String, Date, Array, and more. In addition to these built-in objects, you can also create your own.
An object is just a special kind of data, with a collection of properties and methods.
Let's illustrate with an example: A person is an object. Properties are the values associated with the object. The persons' properties include name, height, weight, age, skin tone, eye color, etc. All persons have these properties, but the values of those properties will differ from person to person. Objects also have methods. Methods are the actions that can be performed on objects. The persons' methods could be eat(), sleep(), work(), play(), etc.

Properties

The syntax for accessing a property of an object is:

objName.propName

You can add properties to an object by simply giving it a value. Assume that the personObj already exists - you can give it properties named firstname, lastname, age, and eyecolor as follows:

personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=30;
personObj.eyecolor="blue";

document.write(personObj.firstname);

The code above will generate the following output:

John

Methods

An object can also contain methods.
You can call a method with the following syntax:

objName.methodName()

Note: Parameters required for the method can be passed between the parentheses.
To call a method called sleep() for the personObj:

personObj.sleep();

Creating Your Own Objects

There are different ways to create a new object:
1. Create a direct instance of an object
The following code creates an new instance of an object, and adds four properties to it:

personObj=new Object();
personObj.firstname="John";
personObj.lastname="Doe";
personObj.age=50;
personObj.eyecolor="blue";

alternative syntax (using object literals):

personObj={firstname:"John",lastname:"Doe",age:50,eyecolor:"blue"};

Adding a method to the personObj is also simple. The following code adds a method called eat() to the personObj:

personObj.eat=eat;

2. Create an object constructor
Create a function that construct objects:

function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;
}

Inside the function you need to assign things to this.propertyName. The reason for all the "this" stuff is that you're going to have more than one person at a time (which person you're dealing with must be clear). That's what "this" is: the instance of the object at hand.
Once you have the object constructor, you can create new instances of the object, like this:

var myFather=new person("John","Doe",50,"blue");
var myMother=new person("Sally","Rally",48,"green");

You can also add some methods to the person object. This is also done inside the function:

function person(firstname,lastname,age,eyecolor)
{
this.firstname=firstname;
this.lastname=lastname;
this.age=age;
this.eyecolor=eyecolor;

this.newlastname=newlastname;
}

Note that methods are just functions attached to objects. Then we will have to write the newlastname() function:

function newlastname(new_lastname)
{
this.lastname=new_lastname;
}

The newlastname() function defines the person's new last name and assigns that to the person. JavaScript knows which person you're talking about by using "this.". So, now you can write: myMother.newlastname("Doe").