Many different events can occur when interacting with a Web page. When the event occurs, the script that's designed to process the event runs. The script itself is called an event handler. Think of properties as adjectives that describe part of the Web page. For example, properties include the width and height of HTML elements, the URL of the document that's being displayed, and the number of frames that are on the page.
Scripts can read and write properties.
For example, you could write a script that changes the color of some text. Or, you could write a script that moves a button across the screen by changing its position properties. Scripts can also call Dynamic HTML methods. For example, you can call the setTimeout method of the window object. This tells Internet Explorer to call some script after a specific delay.