change background image in body

How do i change the background image in CSS at run time? I have the following background image in body and can the image be changed at run time?

body {
height: 100%;
background: #fff8db url(../images/backgrounds/header-top.jpg) no-repeat center top; 
/*background-color: #fff8db;*/
/*background-size: 1650px 900px;*/
font-family: Arial, Verdana, Helvetica, sans-serif; 
font-size:12px; 
font-weight:normal; 
color:#404040;
line-height:20px; }

Answers:

Answer

If you have JQuery loaded already, you can just do this:

$('body').css('background-image', 'url(../images/backgrounds/header-top.jpg)');

EDIT:

First load JQuery in the head tag:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" type="text/javascript"></script>

Then call the Javascript to change the background image when something happens on the page, like when it finishes loading:

<script type="text/javascript">
    $(document).ready(function() {
        $('body').css('background-image', 'url(../images/backgrounds/header-top.jpg)');
    });
</script>
Answer

You would need to use Javascript for this. You can set the style of the background-image for the body like so.

var body = document.getElementsByTagName('body')[0];
body.style.backgroundImage = 'url(http://localhost/background.png)';

Just make sure you replace the URL with the actual URL.

Answer

Just set an onload function on the body:

<body onload="init()">

Then do something like this in javascript:

function init() {
  var someimage = 'changableBackgroudImage';
  document.body.style.background = 'url(img/'+someimage+'.png) no-repeat center center'
}

You can change the 'someimage' variable to whatever you want depending on some conditions, such as the time of day or something, and that image will be set as the background image.

Answer

If you're page has an Open Graph image, commonly used for social sharing, you can use it to set the background image at runtime with vanilla JavaScript like so:

<script>
  const meta = document.querySelector('[property="og:image"]');
  const body = document.querySelector("body");
  body.style.background = `url(${meta.content})`;
</script>

The above uses document.querySelector and Attribute Selectors to assign meta the first Open Graph image it selects. A similar task is performed to get the body. Finally, string interpolation is used to assign body the background.style the value of the path to the Open Graph image.

If you want the image to cover the entire viewport and stay fixed set background-size like so:

body.style.background = `url(${meta.content}) center center no-repeat fixed`;
body.style.backgroundSize = 'cover';

Using this approach you can set a low-quality background image placeholder using CSS and swap with a high-fidelity image later using an image onload event, thereby reducing perceived latency.

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