Form Control JavaScript DHTML
/*
Examples From
JavaScript: The Definitive Guide, Fourth Edition
Legal matters: these files were created by David Flanagan, and are
Copyright (c) 2001 by David Flanagan. You may use, study, modify, and
distribute them for any purpose. Please note that these examples are
provided "as-is" and come with no warranty of any kind.
David Flanagan
*/
// This is the constructor function for our new ToggleButton class.
// Calling it creates a ToggleButton object and outputs the required
// and ![]()
tags into the specified document at the current location.
// Therefore, don't call it for the current document from an event handler.
// Arguments:
// document: The Document object the buttons are be created in.
// checked: A boolean that says whether the button is initially checked.
// label: An optional string that specifies text to appear after the button.
// onclick: An optional function to be called when the toggle button is
// clicked. It is passed a boolean indicating the new
// state of the button. You can also pass a string, which is
// be converted to a function that is passed a boolean argument
// named "state".
function ToggleButton(document, checked, label, onclick)
{
// The first time we are called (and only the first time), we have
// to do some special stuff. First, now that the prototype object
// is created, we can set up our methods.
// Second, we need to load the images we'll be using.
// Doing this gets the images in the cache for when we need them.
if (!ToggleButton.prototype.over) {
// Initialize the prototype object to create our methods.
ToggleButton.prototype.over = _ToggleButton_over;
ToggleButton.prototype.out = _ToggleButton_out;
ToggleButton.prototype.click = _ToggleButton_click;
// Now create an array of image objects, and assign URLs to them.
// The URLs of the images are configurable and are stored in an
// array property of the constructor function itself. They are
// initialized below. Because of a bug in Netscape, we've got
// to maintain references to these images, so we store the array
// in a property of the constructor rather than using a local variable.
ToggleButton.images = new Array(4);
for(var i = 0; i < 4; i++) {
ToggleButton.images[i] = new Image(ToggleButton.width,
ToggleButton.height);
ToggleButton.images[i].src = ToggleButton.imagenames[i];
}
}
// Save some of the arguments we were passed.
this.document = document;
this.checked = checked;
// Remember that the mouse is not currently on top of us.
this.highlighted = false;
// Save the onclick argument to be called when the button is clicked.
// If it is not already a function, attempt to convert it
// to a function that is passed a single argument, named state.
this.onclick = onclick;
if (typeof this.onclick == "string")
this.onclick = new Function("state", this.onclick);
// Figure out what entry in the document.images[] array the images
// for this checkbox will be stored at.
var index = document.images.length;
// Now output the HTML code for this checkbox. Use and ![]()
tags.
// The event handlers we output here are confusing but crucial to the
// operation of this class. The "_tb" property is defined below, as
// are the over(), out(), and click() methods.
document.write('
'onmouseout="document.images[' + index + ']._tb.out()" '+
'onclick="document.images[' + index + ']._tb.click(); return false;">');
document.write('
' height=' + ToggleButton.height +
' border="0" hspace="0" vspace="0" align="absmiddle">');
if (label) document.write(label);
document.write('');
// Now that we've output the ![]()
tag, save a reference to the
// Image object that it created in the ToggleButton object.
this.image = document.images[index];
// And also make a link in the other direction, from the Image object
// to this ToggleButton object. Do this by defining a "_tb" property
// in the Image object.
this.image._tb = this;
}
// This becomes the over() method.
function _ToggleButton_over()
{
// Change the image, and remember that we're highlighted.
this.image.src = ToggleButton.imagenames[this.checked + 2];
this.highlighted = true;
}
// This becomes the out() method.
function _ToggleButton_out()
{
// Change the image, and remember that we're not highlighted.
this.image.src = ToggleButton.imagenames[this.checked + 0];
this.highlighted = false;
}
// This becomes the click() method.
function _ToggleButton_click()
{
// Toggle the state of the button, change the image, and call the
// onclick method, if it was specified for this ToggleButton.
this.checked = !this.checked;
this.image.src = ToggleButton.imagenames[this.checked+this.highlighted*2];
if (this.onclick) this.onclick(this.checked);
}
// Initialize static class properties that describe the checkbox images. These
// are just defaults. Programs can override them by assigning new values.
// But they should only be overridden *before* any ToggleButtons are created.
ToggleButton.imagenames = new Array(4); // Create an array.
ToggleButton.imagenames[0] = "images/button0.gif"; // The unchecked box
ToggleButton.imagenames[1] = "images/button1.gif"; // The box with a check mark
ToggleButton.imagenames[2] = "images/button2.gif"; // Unchecked but highlighted
ToggleButton.imagenames[3] = "images/button3.gif"; // Checked and highlighted
ToggleButton.width = ToggleButton.height = 25; // Size of all images
Optional extras:
// Create ToggleButton objects and output the HTML that implements them.
// One button has no click handler, one has a function, and one has a string.
var tb1 = new ToggleButton(document, true, "56K Modem");
var tb2 = new ToggleButton(document, false, "Laser Printer",
function(clicked) {alert("printer: " + clicked);});
var tb3 = new ToggleButton(document, false, "Tape Backup Unit",
"alert('Tape backup: ' + state)");