By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be detected by Java Script.

Every element on a dynamic or static web page has certain events which can trigger Java Script functions. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks on that button. We define the events in the HTML tags.

Examples of events:

A mouse click

A web page or an image loading

Mousing over a hot spot on the web page

Selecting an input box in an HTML form

Submitting an HTML form

A keystroke

The following table lists the events recognized by JavaScript:

Events are normally used in combination with functions, and the function can not be executed before the event occurs.

The onload and onUnload events are triggered when the user enters or leaves the webpage.

The onload event is often used to check the users browser type and browser version, and load the proper version of the web page based on the information.

Both the onload and onUnload events are also often used to deal with cookies that should be set when a user enters or leaves the page. For example, you could have a popup asking for the visiter's name upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you could have another popup saying something like as: "Welcome Vyom!".

The onBlur, onFocusand and onChange events are often used in combination with validation of form fields.

Here is an example of how to use the onChange event. The checkEmail() function will be called whenever the user changes the content of the field:

The onSubmit event is used to validate ALL form fields before submitting it.

Below is an example of how to use the onSubmit event. The checkForm() function will be called when the user clicks the submit button in the form. If the field values are not accepted, the submit should be cancelled. The function checkForm() returns either true or false. If it returns true the form will be submitted, otherwise the submit will be cancelled:

onMouseOver and onMouseOut are often used to create "animated" buttons.

Below is an example of an onMouseOver event. An alert box appears when an onMouseOver event is detected: