Mega Code Archive
Called from an onmousedown event handler
<![CDATA[
/*
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
*/
/**
* PortableDrag.js:
* beginDrag() is designed to be called from an onmousedown event handler.
* elementToDrag may be the element that received the mousedown event, or it
* may be some containing element. event must be the Event object for the
* mousedown event. This implementation works with both the DOM Level 2
* event model and the IE Event model.
**/
function beginDrag(elementToDrag, event) {
// Compute the distance between the upper-left corner of the element
// and the mouse click. The moveHandler function below needs these values.
var deltaX = event.clientX - parseInt(elementToDrag.style.left);
var deltaY = event.clientY - parseInt(elementToDrag.style.top);
// Register the event handlers that will respond to the mousemove events
// and the mouseup event that follow this mousedown event.
if (document.addEventListener) { // DOM Level 2 Event Model
// Register capturing event handlers
document.addEventListener("mousemove", moveHandler, true);
document.addEventListener("mouseup", upHandler, true);
}
else if (document.attachEvent) { // IE 5+ Event Model
// In the IE Event model, we can't capture events, so these handlers
// are triggered when only if the event bubbles up to them.
// This assumes that there aren't any intervening elements that
// handle the events and stop them from bubbling.
document.attachEvent("onmousemove", moveHandler);
document.attachEvent("onmouseup", upHandler);
}
else { // IE 4 Event Model
// In IE 4 we can't use attachEvent(), so assign the event handlers
// directly after storing any previously assigned handlers so they
// can be restored. Note that this also relies on event bubbling.
var oldmovehandler = document.onmousemove;
var olduphandler = document.onmouseup;
document.onmousemove = moveHandler;
document.onmouseup = upHandler;
}
// We've handled this event. Don't let anybody else see it.
if (event.stopPropagation) event.stopPropagation(); // DOM Level 2
else event.cancelBubble = true; // IE
// Now prevent any default action.
if (event.preventDefault) event.preventDefault(); // DOM Level 2
else event.returnValue = false; // IE
/**
* This is the handler that captures mousemove events when an element
* is being dragged. It is responsible for moving the element.
**/
function moveHandler(e) {
if (!e) e = window.event; // IE event model
// Move the element to the current mouse position, adjusted as
// necessary by the offset of the initial mouse click.
elementToDrag.style.left = (e.clientX - deltaX) + "px";
elementToDrag.style.top = (e.clientY - deltaY) + "px";
// And don't let anyone else see this event.
if (e.stopPropagation) e.stopPropagation(); // DOM Level 2
else e.cancelBubble = true; // IE
}
/**
* This is the handler that captures the final mouseup event that
* occurs at the end of a drag.
**/
function upHandler(e) {
if (!e) e = window.event; // IE event model
// Unregister the capturing event handlers.
if (document.removeEventListener) { // DOM Event Model
document.removeEventListener("mouseup", upHandler, true);
document.removeEventListener("mousemove", moveHandler, true);
}
else if (document.detachEvent) { // IE 5+ Event Model
document.detachEvent("onmouseup", upHandler);
document.detachEvent("onmousemove", moveHandler);
}
else { // IE 4 Event Model
document.onmouseup = olduphandler;
document.onmousemove = oldmovehandler;
}
// And don't let the event propagate any further.
if (e.stopPropagation) e.stopPropagation(); // DOM Level 2
else e.cancelBubble = true; // IE
}
}
]]>