Mousedown event handler of an object within a Layer
/* 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 */
<script> /** * This function is intended for use in a mousedown event handler of an object * within a Layer. The first argument must be a Layer object. The second * argument must be the Event object for the mousedown event. **/ function beginDrag(layerToDrag, event) { // This nested function responds to mousemove events and moves the layer. function moveHandler(event) { // Move the element to the current mouse position, adjusted as // necessary by the offset of the initial mouse click. layerToDrag.moveTo(event.pageX - deltaX, event.pageY-deltaY);
// Don't take any default action, and don't propagate further. return false; }
// This nested function handles mouseup events. // It stops capturing events, and de-register the handlers. function upHandler(event) { // Stop capturing and handling drag events document.releaseEvents(Event.MOUSEMOVE | Event.MOUSEUP); document.onmousemove = null; document.onmouseup = null;
// Don't take any default action, and don't propagate further. return false; }
// Compute the distance between the upper left of the layer and and the // mouse click. The moveHandler function below needs these values. var deltaX = event.pageX - layerToDrag.left; var deltaY = event.pageY - layerToDrag.top;
// Arrange to capture mousemove and mouseup events. // Then arrange to handle them using the functions defined below. document.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP); document.onmousemove = moveHandler; document.onmouseup = upHandler; } </script> <!-- Here's how we might use beginDrag() in Netscape 4 --> <!-- Define a layer using CSS attributes --> <div id="div1" style="position:absolute; left:100px; top:100px;"> <!-- Give the layer some content, and a mousedown event handler --> <img src="images/plus.gif" width="20" height="20" onmousedown="if (event.modifiers & Event.SHIFT_MASK) beginDrag(window.document.div1, event);"> </div>
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