Web Programming Step by Step

Lecture 18
More Events and Validation

Reading: 9.2 - 9.3

Except where otherwise noted, the contents of this presentation are Copyright 2009 Marty Stepp and Jessica Miller.

Valid XHTML 1.1 Valid CSS!

Page/window events (9.2.5)

load the browser loads the page
unload the browser exits the page
resize the browser window is resized
contextmenu the user right-clicks to pop up a context menu
error an error occurs when loading a document or an image
// best way to attach event handlers on page load
window.onload = function() { ... };
document.observe("dom:loaded", function() {
	$("orderform").observe("submit", verify);

Form events (9.2.4)

event name description
submit form is being submitted
reset form is being reset
change the text or state of a form control has changed
window.observe("load", function() {
	$("orderform").observe("submit", verify);

function verify(event) {
	if ($("zipcode").value.length < 5) {
		event.stop();       // cancel form submission unless
	}                     // zip code is 5 chars long

Prototype and forms (9.1.6)

activate clear disable enable
focus getValue present select

Client-side validation code

<form id="exampleform" action="http://foo.com/foo.php">
window.onload = function() {
	$("exampleform").onsubmit = checkData;

function checkData(event) {
	if ($("city").value == "" || $("state").value.length != 2) {
		alert("Error, invalid city/state.");  // show error message 

Regular expressions in JavaScript

Replacing text with regular expressions

  • string.replace(regex, "text")
    • replaces the first occurrence of given pattern with the given text
    • var str = "Marty Stepp";
      str.replace(/[a-z]/, "x") returns "Mxrty Stepp"
    • returns the modified string as its result; must be stored
      str = str.replace(/[a-z]/, "x")
  • a g can be placed after the regex for a global match (replace all occurrences)
    • str.replace(/[a-z]/g, "x") returns "Mxxxx Sxxxx"
  • using a regex as a filter
    • str = str.replace(/[^A-Z]+/g, "") turns str into "MS"

Keyboard/text events (9.2.3)

name description
keydown user presses a key while this element has keyboard focus
keyup user releases a key while this element has keyboard focus
keypress user presses and releases a key while this element has keyboard focus
focus this element gains keyboard focus
blur this element loses keyboard focus
select this element's text is selected or deselected)
  • focus: the attention of the user's keyboard (given to one element at a time)

Key event objects

property name description
keyCode ASCII integer value of key that was pressed
(convert to char with String.fromCharCode)
altKey, ctrlKey, shiftKey true if Alt/Ctrl/Shift key is being held
Prototype's key code constants
  • issue: if the event you attach your listener to doesn't have the focus, you won't hear the event
    • possible solution: attach key listener to entire page body, outer element, etc.