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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 17-4 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 17-4 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>/** * Drag.js: drag absolutely positioned HTML elements. * * This module defines a single drag() function that is designed to be called * from an onmousedown event handler. Subsequent mousemove events will * move the specified element. A mouseup event will terminate the drag. * If the element is dragged off the screen, the window does not scroll. * This implementation works with both the DOM Level 2 event model and the * IE event model. * * Arguments: * * elementToDrag: the element that received the mousedown event or * some containing element. It must be absolutely positioned. Its * style.left and style.top values will be changed based on the user's * drag. * * event: the Event object for the mousedown event. **/function drag(elementToDrag, event) { // The mouse position (in window coordinates) // at which the drag begins var startX = event.clientX, startY = event.clientY; // The original position (in document coordinates) of the // element that is going to be dragged. Since elementToDrag is // absolutely positioned, we assume that its offsetParent is the // document body. var origX = elementToDrag.offsetLeft, origY = elementToDrag.offsetTop; // Even though the coordinates are computed in different // coordinate systems, we can still compute the difference between them // and use it in the moveHandler() function. This works because // the scrollbar position never changes during the drag. var deltaX = startX - origX, deltaY = startY - origY; // 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 capture events by calling // setCapture() on the element to capture them. elementToDrag.setCapture(); elementToDrag.attachEvent("onmousemove", moveHandler); elementToDrag.attachEvent("onmouseup", upHandler); // Treat loss of mouse capture as a mouseup event elementToDrag.attachEvent("onlosecapture", upHandler); } else { // IE 4 Event Model // In IE 4 we can't use attachEvent() or setCapture(), so we set // event handlers directly on the document object and hope that the // mouse events we need will bubble up. var oldmovehandler = document.onmousemove; // used by upHandler() 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 elementToDrag.detachEvent("onlosecapture", upHandler); elementToDrag.detachEvent("onmouseup", upHandler); elementToDrag.detachEvent("onmousemove", moveHandler); elementToDrag.releaseCapture(); } else { // IE 4 Event Model // Restore the original handlers, if any 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 }}</pre><div class="lefttitle" style="padding:0px; text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><p><script type="text/javascript">amazon_ad_tag="davidflanagancom"; amazon_ad_width="300"; amazon_ad_height="250"; amazon_ad_logo="hide";</script><script type="text/javascript" src="../../www.assoc-amazon.com/s/ads.js" tppabs="http://www.assoc-amazon.com/s/ads.js"></script></div></body></html>⌨️ 快捷键说明
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