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This is really for informational and learning purposes while learning more about JavaScript and CSS. I have a local browser index page that I wanted to rotate the background image onload. After looking around and playing with different solutions, I settled on this for the basic rotate functionality:

<html>
<head>
<script language="javascript" type="text/javascript">
function rotate()
{
   var imgArray = new Array("img1.jpg", "img2.jpg", "img3.jpg");
   var aImg = Math.floor(Math.random()*imgArray.length);
   var img = imgArray[aImg];
   document.body.style.background = "url(" + img + ") no-repeat";
   document.body.style.backgroundSize = "cover";
}
</script>
</head>
<body onload="rotate()">
</body>
</html>

During the process, before I just set the backgroundSizeas cover to fill the window, I was playing with the idea of resizing the images before setting them as the background image after they are selected from the array.

I have done a lot of searching, and the only real working solutions I have found rely on selecting the element by ID, but that also requires that the image has an ID associated, such as in the IMG property in the HTML code. Here the image is selected and set in the JavaScript with CSS.

I have tried setting the image dimensions with img.width / img.height and img.style.width / img.style.height, as well as a few other random solutions I have e across, but whenever I try to change these the image either does not change or it does not show at all.

function rotate()
{
   var imgArray = new Array("img1.jpg", "img2.jpg", "img3.jpg");
   var aImg = Math.floor(Math.random()*imgArray.length);
   var img = imgArray[aImg];
   image = rsize(img);
   document.body.style.background = "url(" + image + ") no-repeat";
   document.body.style.backgroundSize = "cover";
}
function rsize(image)
{
   image.style.width = "300px";
   image.style.height = "300px";
   return image;
}

I know I am probably doing something wrong here. Is there a way, in this circumstance, that I can resize these images? Or is there a better way to construct this?

Thanks in advance.

This is really for informational and learning purposes while learning more about JavaScript and CSS. I have a local browser index page that I wanted to rotate the background image onload. After looking around and playing with different solutions, I settled on this for the basic rotate functionality:

<html>
<head>
<script language="javascript" type="text/javascript">
function rotate()
{
   var imgArray = new Array("img1.jpg", "img2.jpg", "img3.jpg");
   var aImg = Math.floor(Math.random()*imgArray.length);
   var img = imgArray[aImg];
   document.body.style.background = "url(" + img + ") no-repeat";
   document.body.style.backgroundSize = "cover";
}
</script>
</head>
<body onload="rotate()">
</body>
</html>

During the process, before I just set the backgroundSizeas cover to fill the window, I was playing with the idea of resizing the images before setting them as the background image after they are selected from the array.

I have done a lot of searching, and the only real working solutions I have found rely on selecting the element by ID, but that also requires that the image has an ID associated, such as in the IMG property in the HTML code. Here the image is selected and set in the JavaScript with CSS.

I have tried setting the image dimensions with img.width / img.height and img.style.width / img.style.height, as well as a few other random solutions I have e across, but whenever I try to change these the image either does not change or it does not show at all.

function rotate()
{
   var imgArray = new Array("img1.jpg", "img2.jpg", "img3.jpg");
   var aImg = Math.floor(Math.random()*imgArray.length);
   var img = imgArray[aImg];
   image = rsize(img);
   document.body.style.background = "url(" + image + ") no-repeat";
   document.body.style.backgroundSize = "cover";
}
function rsize(image)
{
   image.style.width = "300px";
   image.style.height = "300px";
   return image;
}

I know I am probably doing something wrong here. Is there a way, in this circumstance, that I can resize these images? Or is there a better way to construct this?

Thanks in advance.

  • javascript
  • html
  • css
  • image-resizing
Share Improve this question edited Jun 7, 2012 at 17:02 Bergi 667k161 gold badges1k silver badges1.5k bronze badges asked Jun 7, 2012 at 16:55 jb11jb11 1612 silver badges10 bronze badges
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2 Answers 2

Reset to default 5

You must set image.style.width and image.style.height on an actual image DOM object, not on the URL as you are currently trying to do.

As an image object is not used for background images, you can't really directly do what you're trying to do for a background image.

You could use the CSS background-size property, but that is fairly new and is not supported in versions of IE prior to IE9. If you were using that, you would set the actual size for that, not "cover".

You could also use an actual DOM image and then present that DOM image as centered in your page if that's what you're really trying to do.

For example, here's how you create a DOM image object, assign it a URL, set it's size and insert it into your page:

var imgArray = new Array("img1.jpg", "img2.jpg", "img3.jpg");
var aImg = Math.floor(Math.random()*imgArray.length);
var imgURL = imgArray[aImg];
var img = new Image();
img.src = imgURL; 
img.style.width = "300px";
img.style.height = "300px";
img.id = "centeredImage";
document.body.appendChild(img);

You could then use CSS to position is in the center of your page if you wanted.

Working demo here: http://jsfiddle/jfriend00/jqMtV/

No, you have no <img> elements you could (re)size (btw, they would not need ids to be selectable). Your use of rsize(imgArray[aImg]) operates on the array members, which are strings and not DOM elements, so setting values on their non-existent style property would throw an error.

Yet, you're already on the right way with using the backgroundSize style property. Just don't set it to cover, but to the size you need!

document.body.style.backgroundSize = "300px 300px";

If you would want to use a <img> element, add this at the end of your <body>:

<img src="some.jpg" style="position:fixed; z-index:-1; width:100%; height:100%" />

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