Fix for background-position in IE

问题

I get this problem in IE7 when running a piece of code that uses jquery and 2 jquery plugins. The code works in FF3 and Chrome.

The full error is:

Line: 33 
Char: 6 
Error: bg is null or not an object 
Code: 0 
URL: http://localhost/index2.html

However line 33 is a blank line.

I am using 2 plugins: draggable and zoom. No matter what I do to the code it is always line 33 that is at fault. I check the source has update via view source but I feel this could be lying to me.

<body>
<div id="zoom" class="zoom"></div>
<div id="draggable" class="main_internal"><img src="tiles/mapSpain-smaller.jpg" alt=""></div>

<script type="text/javascript">
$(document).ready(function() {
    $('#draggable').drag();
    $('#zoom').zoom({target_div:"draggable", zoom_images:new Array('tiles/mapSpain-smaller.jpg', 'tiles/mapSpain.jpg') });
});
</script>

</body>

Essentially what I am trying to do is recreate the Pragmatic Ajax map demo with jQuery.

It would appear that the second line of this snippet is causing the trouble:

bg = $(this).css('background-position');                    
if(bg.indexOf('%')>1){

It seems to be trying to select the background-position property of #draggable and not finding it? Manually adding a background-position: 0 0; didn't fix it. Any ideas on how to get around this problem?

I tried using the MS Script Debugger but that is nearly useless. Can't inspect variables or anything else.

回答1:

A bit more digging about on the Interweb has revealed the answer: IE doesn't understand the selector background-position. It understands the non-standard background-position-x and background-position-y.

Currently hacking something together to workaround it.

Nice one, Redmond.

回答2:

To get around the fact that Internet Explorer does not support the "background-position" CSS attribute, as of jQuery 1.4.3+ you can use the .cssHooks object to normalize this attribute between browsers.

To save yourself some time, there is a background position jQuery plugin available that allows both "background-position" and "background-position-x/y" to work as expected in browsers that don't support one or the other by default.

回答3:

It is interesting. IE8 doesn't understand getter backgroundPosition, but it understands setter.

$('.promo3').mousewheel(function(e,d){
  var promo3 = $(this);
  var p = promo3.css('backgroundPosition');
  if (p === undefined) {
    p = promo3.css('backgroundPositionX') + ' ' + promo3.css('backgroundPositionY');
  }
  var a = p.split(' ');
  var y = parseInt(a[1]);
  if (d > 0) {
    if (y < -1107) y += 1107; 
    y -= 40;
  }
  else {
    if (y > 1107) y -= 1107;
    y += 40;
  }
  promo3.css('backgroundPosition', a[0] + ' ' + y + 'px');
  return false;
});

It works great in IE8 and IE8 compatible view.

回答4:

This worked for me:

    if (navigator.appName=='Microsoft Internet Explorer')
   {
    bg = $(drag_div).css('backgroundPositionX') + " " + $(drag_div).css('backgroundPositionY');
   }
   else
   {
    bg = $(drag_div).css('background-position');
   }

hope it does for you.

回答5:

You may want to check to make sure that you are loading your js files in the correct order so that any dependencies are taken into account.

回答6:

A bit of thinking (and a cup of tea) later I came up with:

if(bg == 'undefined' || bg == null){
    bg = $(this).css('background-position-x') + " " + $(this).css('background-position-y');
}

Unfortunately it returns center center despite the online resources I can find state it should return 0 0 if the values are undefined.

Beginning to wonder if there is an actual fix/workaround to this. A lot of people have tried and all so far fail to catch all edge cases.

The camelCase version of backgroundPosition seems viable but I don't know enough of jQuery to make an accurate assessment of how to go about it - from what I have read you can only use camelCase as getters if the property has been set previously. Please tell me if I am mistaken.

回答7:

However line 33 is a blank line.

It'll be line 33 of one of your .js files, not line 33 of the HTML itself. IE fails to report which actual file the error was in. Look at line 33 of each .js for something about ‘bg’; if the worst comes to the worst you can start inserting newlines at the start of each .js and see whether the line number changes.

I check the source has update via view source but I feel this could be lying to me.

View source will always show you what IE got from the server. It won't show any updates to the DOM.

回答8:

try backgroundPosition istead

Also, make sure that 'this' exists and that your request for an attribute returns a value. IE will throw this kind of errors when you try to call a method on a property that does not exist, therefore bg is null or null an object. if you dont care about IE you can do bg = $(this)... || '' so that theres always something referenced.

Also, unrelated to the error you're getting, but is your index value of 1 correct? Did you mean -1 ?

回答9:

Yupp,
Try background-position instead or just set the background-position with jquery before you call it. Ill guess one often knows the positions through CSS before calling it. It isnt pretty, but somehow it did the trick for me.)

eg:

//set it in with javascript.
$("someid").css("background-position", "10px 0");
...
//do some funky stuff
//call it
$("someid").css("background-position");
//and it would return "10px 0" even in IE7

回答10:

if nothing helps, it's also possible to make the following trick.

We can replace a background of an element by an inner absolutely positioned element (with the same background). The coordinates will be replaced by left and top properties. This will work in all browsers.

For better understanding, please, check the code:

Before

<div></div>

div {
  background: url(mySprite.png);
  background-position: -100px 0;
}

After

<div>
  <span></span>
</div>

div {
  position: relative;
  overflow: hidden;
  width: 100px;       /* required width to show a part of your sprite */
  height: 100px;      /* required height ... */
}

div span {
  position: absolute;
  left: -100px;       /* bg left position */
  top: 0;             /* bg top position */
  display: block;
  width: 500px;       /* full sprite width */
  height: 500px;      /* full sprite height */
  background: url(mySprite.png);
}

This solution is not very flexible, but it helped me to show icons hover state properly.

回答11:

You can't use dashes in the jquery css function. You have to do it in camelCase: .css('backgroundPosition') or .css('backgroundPositionX') and .css('backgroundPositionY') for IE

来源：https://stackoverflow.com/questions/594870/fix-for-background-position-in-ie

标签

javascript

jquery

internet-explorer

background-position