FYBSC IT Web Programming Unit III Events and Event Handlers
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The document explains HTML events and how JavaScript can react to them, describing events triggered by users or the browser. It outlines the syntax for adding event handlers to HTML elements and provides examples of common events like onclick and onchange. Lastly, it highlights the capabilities of JavaScript in handling user interactions and actions on a web page.
FYBSC IT Web Programming Unit III Events and Event Handlers
- 2. JAVASCRIPT EVENTS • HTML events are "things" that happen to HTML elements. • When JavaScript is used in HTML pages, JavaScript can "react" on these events.
- 3. HTML EVENTS • An HTML event can be something the browser does, or something a user does. • Here are some examples of HTML events: • An HTML web page has finished loading • An HTML input field was changed • An HTML button was clicked • Often, when events happen, you may want to do something. • JavaScript lets you execute code when events are detected. • HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.
- 4. HTML EVENTS SYNTAX • With single quotes: <some-HTML-element some-event='some JavaScript'> • With double quotes: <some-HTML-element some-event="some JavaScript"> • Example • In the following example, an onclickattribute (with code), is added to a button element: <button onclick="document.getElementById('demo').innerHTML = Date()">The time is?</button>
- 5. ONCLICK EVENT <!DOCTYPE html> <html> <body> <button onclick="document.getElementById('demo').innerHTML=Date()">The time is?</button> <p id="demo"></p> </body> </html>
- 6. COMMON HTML EVENTS Event Description onchange An HTML element has been changed onclick The user clicks an HTML element onmouseover The user moves the mouse over an HTML element onmouseout The user moves the mouse away from an HTML element onkeydown The user pushes a keyboard key onload The browser has finished loading the page
- 7. WHAT CAN JAVASCRIPT DO? • Event handlers can be used to handle, and verify, user input, user actions, and browser actions: • Things that should be done every time a page loads • Things that should be done when the page is closed • Action that should be performed when a user clicks a button • Content that should be verified when a user inputs data • And more ...