Electronic Books

To illustrate the use of an external library in JavaScript a simple class Panel is defined in the external
.js file. The class accepts the name of an element (attribute id in the HTML element) as argument for its
constructor and is able to perform some simple actions on the element such as dragging it and switching
its visibility.
// content of file external.js
function Panel(name)
{
var el = document.getElementById(name);
this.el = el;
el.style.left = el.style.left || el.offsetLeft;
el.style.top = el.style.top || el.offsetTop;
this.visible = true;
this.draggable = false;
}
Panel.prototype.activateDrag = function()
{
var el = this.el;
el.style.backgroundColor = ???#eeeeee???;
el.onmousedown = function(e) {
e = e || event; // normalize event
if(!e) return; // no compatible browser
var pos = {
x : parseInt(el.style.left),
y : parseInt(el.style.top),
h : e.clientX,
v : e.clientY }
document.onmouseup = function(e)
{
document.onmousemove = null;
}
document.onmousemove = function(e)
{
if(!e) e = event; // normalize event
el.


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