March 27, 2012
How to move an element styled by CSS stylesheet?
Question by shortspider
I have an image that I want to move. I can move the element with javascript if I have the HTML below:
<html>
<head>
<title>Snake</title>
<script type="text/javascript" src="snake.js"></script>
<!-- <link type="text/css" href="snake.css"> -->
</head>
<body onKeyPress="ProcessKeypress(event);">
<p><img id="snake" style="z-index: 0; left: 300px; position: absolute; top: 250px"
float=top border=0 hspace=0 src="snake.gif"></p>
</body>
However I want to stye the image element using CSS. When I do this my code to move the image does not work. HTML and CSS below are what I would like to use.
<html>
<head>
<title>Snake</title>
<script type="text/javascript" src="snake.js"></script>
<link type="text/css" href="snake.css">
</head>
<body onKeyPress="ProcessKeypress(event);">
<p><img id="snake" src="snake.gif"></p>
</body>
@CHARSET "UTF-8";
img {
z-index: 0;
left: 300px;
position: absolute;
top: 250px;
float: top;
border: 0;
hspace: 0;
}
JavaScript below is what I am using to move the image. Any and all help appreciated.
function moveObj(name, Xpix, Ypix)
{
obj = document.getElementById(name);
px = parseInt(obj.style.left) + Xpix;
py = parseInt(obj.style.top) + Ypix;
obj.style.left = px;
obj.style.top = py;
}
function ProcessKeypress(e)
{
var myObj = 'snake';
var moveBy = 10;
if(e.keyCode === 97) {
moveObj(myObj, -moveBy, 0);
}
else if(e.keyCode === 100) {
moveObj(myObj, moveBy, 0);
}
else if(e.keyCode === 115) {
moveObj(myObj, 0, moveBy);
}
else if(e.keyCode === 119) {
moveObj(myObj, 0, -moveBy);
}
}
Answer by Starx
obj.style.left accesses the style properties defined in inline only.
UPDATE
Here is your pure JavaScript Solution
Function: getStyleProp() to get the current applied style [Source]
function getStyleProp(elem, prop){
if(window.getComputedStyle)
return window.getComputedStyle(elem, null).getPropertyValue(prop);
else if(elem.currentStyle) return elem.currentStyle[prop]; //IE
}
Function: moveObj()
function moveObj(obj, Xpix, Ypix) {
obj.style.left = parseInt(getStyleProp(obj,'left')) + Xpix+"px";
obj.style.top= parseInt(getStyleProp(obj,'top')) + Ypix + "px";
}
Function: ProcessKeypress()
function ProcessKeypress(e) {
var myObj = document.getElementById("snake");
var moveBy = 10;
switch(e.charCode) {
case 97: moveObj(myObj, -moveBy, 0); break;
case 100: moveObj(myObj, moveBy, 0); break;
case 115: moveObj(myObj, 0, moveBy); break;
case 119: moveObj(myObj, 0, -moveBy); break;
}
}
I also solved your case using jQuery: Demo
Function moveObj
function moveObj(obj, Xpix, Ypix) {
obj.css('left', parseInt(obj.css('left')) + Xpix);
obj.css('top', parseInt(obj.css('top')) + Ypix);
}
Function ProcessKeypress
function ProcessKeypress(e) {
var myObj = $("#snake"); //It will be better if it is cached
var moveBy = 10;
switch(e.charCode) { //used Switch for better manageability
case 97: moveObj(myObj, -moveBy, 0); break;
case 100: moveObj(myObj, moveBy, 0); break;
case 115: moveObj(myObj, 0, moveBy); break;
case 119: moveObj(myObj, 0, -moveBy); break;
}
}
Event Trigger attached to document instead
$(document).on('keypress', ProcessKeypress);
