Preloading images with jQuery

Preloading images with jQuery

I’m looking for a quick and easy way to preload images with JavaScript. I’m using jQuery if that’s important.
I saw this here (http://nettuts.com…):
function complexLoad(config, fileNames) {
for (var x = 0; x < fileNames.length; x++) { $("“).attr({
id: fileNames[x],
src: config.imgDir + fileNames[x] + config.imgFormat,
title: “The ” + fileNames[x] + ” nebula”
}).appendTo(“#” + config.imgContainer).css({ display: “none” });
}
};

But, it looks a bit over-the-top for what I want!
I know there are jQuery plugins out there that do this but they all seem a bit big (in size); I just need a quick, easy and short way of preloading images!

Solutions/Answers:

Solution 1:

Quick and easy:

function preload(arrayOfImages) {
    $(arrayOfImages).each(function(){
        $('<img/>')[0].src = this;
        // Alternatively you could use:
        // (new Image()).src = this;
    });
}

// Usage:

preload([
    'img/imageName.jpg',
    'img/anotherOne.jpg',
    'img/blahblahblah.jpg'
]);

Or, if you want a jQuery plugin:

$.fn.preload = function() {
    this.each(function(){
        $('<img/>')[0].src = this;
    });
}

// Usage:

$(['img1.jpg','img2.jpg','img3.jpg']).preload();

Solution 2:

Here’s a tweaked version of the first response that actually loads the images into DOM and hides it by default.

function preload(arrayOfImages) {
    $(arrayOfImages).each(function () {
        $('<img />').attr('src',this).appendTo('body').css('display','none');
    });
}

Solution 3:

Use JavaScript Image object.

This function allows you to trigger a callback upon loading all pictures. However, note that it will never trigger a callback if at least one resource is not loaded. This can be easily fixed by implementing onerror callback and incrementing loaded value or handling the error.

var preloadPictures = function(pictureUrls, callback) {
    var i,
        j,
        loaded = 0;

    for (i = 0, j = pictureUrls.length; i < j; i++) {
        (function (img, src) {
            img.onload = function () {                               
                if (++loaded == pictureUrls.length && callback) {
                    callback();
                }
            };

            // Use the following callback methods to debug
            // in case of an unexpected behavior.
            img.onerror = function () {};
            img.onabort = function () {};

            img.src = src;
        } (new Image(), pictureUrls[i]));
    }
};

preloadPictures(['http://foo/picture.bar', 'http://foo/picture.bar', 'http://foo/picture.bar', 'http://foo/picture.bar'], function(){
    console.log('a');
});

preloadPictures(['http://foo/picture.bar', 'http://foo/picture.bar', 'http://foo/picture.bar', 'http://foo/picture.bar'], function(){
    console.log('b');
});

Solution 4:

JP, After checking your solution, I was still having issues in Firefox where it wouldn’t preload the images before moving along with loading the page. I discovered this by putting some sleep(5) in my server side script. I implemented the following solution based off yours which seems to solve this.

Basically I added a callback to your jQuery preload plugin, so that it gets called after all the images are properly loaded.

// Helper function, used below.
// Usage: ['img1.jpg','img2.jpg'].remove('img1.jpg');
Array.prototype.remove = function(element) {
  for (var i = 0; i < this.length; i++) {
    if (this[i] == element) { this.splice(i,1); }
  }
};

// Usage: $(['img1.jpg','img2.jpg']).preloadImages(function(){ ... });
// Callback function gets called after all images are preloaded
$.fn.preloadImages = function(callback) {
  checklist = this.toArray();
  this.each(function() {
    $('<img>').attr({ src: this }).load(function() {
      checklist.remove($(this).attr('src'));
      if (checklist.length == 0) { callback(); }
    });
  });
};

Out of interest, in my context, I’m using this as follows:

$.post('/submit_stuff', { id: 123 }, function(response) {
  $([response.imgsrc1, response.imgsrc2]).preloadImages(function(){
    // Update page with response data
  });
});

Hopefully this helps someone who comes to this page from Google (as I did) looking for a solution to preloading images on Ajax calls.

Solution 5:

This one line jQuery code creates (and loads) a DOM element img without showing it:

$('<img src="img/1.jpg"/>');

Solution 6:

$.fn.preload = function (callback) {
  var length = this.length;
  var iterator = 0;

  return this.each(function () {
    var self = this;
    var tmp = new Image();

    if (callback) tmp.onload = function () {
      callback.call(self, 100 * ++iterator / length, iterator === length);
    };

    tmp.src = this.src;
  });
};

The usage is quite simple:

$('img').preload(function(perc, done) {
  console.log(this, perc, done);
});

http://jsfiddle.net/yckart/ACbTK/