Advanced Event Handling Techniques in JavaScript
Learn advanced event handling techniques in JavaScript such as accessing event objects, handling mouse events, creating draggable elements, and implementing cleaner code using event delegation and prototypes. Explore examples and best practices for efficient event management in web development.
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Access to Event Object event variable (HTML): <div onclick="mouseClick(event);"> Passed as argument to function (DOM/Firefox): element.onclick = mouseClick; function mouseClick(evt) { ... x = evt.clientX; ... } Global variable (DOM/IE): element.onclick = mouseClick; function mouseClick() { ... x = window.event.clientX; ... } CS 142 Lecture Notes: Events Slide 1
Draggable Rectangle <style type="text/css"> #div1 { position: absolute; } </style> ... <div id="div1" onmousedown="mouseDown(event);" onmousemove="mouseMove(event);" onmouseup="mouseUp(event);">Drag Me!</div> CS 142 Lecture Notes: Events Slide 2
Dragging Application isMouseDown = false; function mouseDown(event) { prevX = event.clientX; prevY = event.clientY; isMouseDown = true; } function mouseMove(event) { if (!isMouseDown) { return; } var element = document.getElementById("div1"); element.style.left = (element.offsetLeft + (event.clientX - prevX)) + "px"; element.style.top = (element.offsetTop + (event.clientY - prevY)) + "px"; prevX = event.clientX; prevY = event.clientY; } function mouseUp(event) { isMouseDown = false; } Slide 3
Cleaner Implementation <body> <div id="div1">Drag Me!</div> <div id="div2">Drag Me Too!</div> <script type="text/javascript" src="dragger.js" /> <script type="text/javascript"> //<![CDATA[ new Dragger("div1"); new Dragger("div2"); //]]> </script> </body>} CS 142 Lecture Notes: Events Slide 4
Dragger.js, part 1 function Dragger(id) { this.isMouseDown = false; this.element = document.getElementById(id); var obj = this; this.element.onmousedown = function(event) { obj.mouseDown(event); } } Dragger.prototype.mouseDown = function(event) { var obj = this; this.oldMoveHandler = document.body.onmousemove; document.body.onmousemove = function(event) { obj.mouseMove(event); } this.oldUpHandler = document.body.onmouseup; document.body.onmouseup = function(event) { obj.mouseUp(event); } this.prevX = event.clientX; this.prevY = event.clientY; this.isMouseDown = true; } CS 142 Lecture Notes: Events Slide 5
Dragger.js, part 2 Dragger.prototype.mouseMove = function(event) { if (!this.isMouseDown) { return; } this.element.style.left = (this.element.offsetLeft + (event.clientX - this.prevX)) + "px"; this.element.style.top = (this.element.offsetTop + (event.clientY - this.prevY)) + "px"; this.prevX = event.clientX; this.prevY = event.clientY; } Dragger.prototype.mouseUp = function(event) { this.isMouseDown = false; document.body.onmousemove = this.oldMoveHandler; document.body.onmouseup = this.oldUpHandler; } CS 142 Lecture Notes: Events Slide 6
Which Element Gets Event? <body> <table> <tr> <td>xyz</td> </tr> </table> </body> Click on this CS 142 Lecture Notes: Events Slide 7
CS 142 Lecture Notes: Cookies Slide 8
