Calling a function when the background image finishes loading

I am loading a remote file 开发者_JAVA百科as a background image, and it could take up to 2 seconds, depending on the internet connection.

I would like to trigger a function when the background image completes loading.

It would work something like this (although this obviously does not)

$("body").css("background image","url('very_big_remote_image')",
         function(data){alert("done")}
         );

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Try this, basically I load an image object and set its source to the background. Once it has loaded I change the background and fire the callback:

var img = new Image();
img.onload = function() {
    $("body").addClass("bg");
    //the callback function call here
};
img.src = 'very_big_remote_image';

This image is never shown, just forces browser to load it then it is cached.

Then have this in your css:

body.bg {
    /* change the position or repeat or whatever else you need in this line */
    background: url('/path/to/the/image/above.jpg') no-repeat 0 0 transparent;
}

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jQuery has a load event function with a callback mechanism:

$("<img />").attr('src', 'img/pic.png').load(function() { /* Do stuff */ });

There are a number of variations.

http://jquery-howto.blogspot.com/2009/02/preload-images-with-jquery.html

http://api.jquery.com/load-event/