I want to know when an image has finished loading. Is there a way to do it with a callback?

If not, is there a way to do it at all?

1

10 Answers

.complete + callback

This is a standards compliant method without extra dependencies, and waits no longer than necessary:

var img = document.querySelector('img') function loaded() { alert('loaded') } if (img.complete) { loaded() } else { img.addEventListener('load', loaded) img.addEventListener('error', function() { alert('error') }) }

Source:

4

Image.onload() will often work.

To use it, you'll need to be sure to bind the event handler before you set the src attribute.

Related Links:

Example Usage:

 window.onload = function () { var logo = document.getElementById('sologo'); logo.onload = function () { alert ("The image has loaded!"); }; setTimeout(function(){ logo.src = ' }, 5000); };
 <html> <head> <title>Image onload()</title> </head> <body> <img src="#" alt="This image is going to load"/> <script type="text/javascript"> </script> </body> </html>
13

You can use the .complete property of the Javascript image class.

I have an application where I store a number of Image objects in an array, that will be dynamically added to the screen, and as they're loading I write updates to another div on the page. Here's a code snippet:

var gAllImages = []; function makeThumbDivs(thumbnailsBegin, thumbnailsEnd) { gAllImages = []; for (var i = thumbnailsBegin; i < thumbnailsEnd; i++) { var theImage = new Image(); theImage.src = "thumbs/" + getFilename(globals.gAllPageGUIDs[i]); gAllImages.push(theImage); setTimeout('checkForAllImagesLoaded()', 5); window.status="Creating thumbnail "+(i+1)+" of " + thumbnailsEnd; // make a new div containing that image makeASingleThumbDiv(globals.gAllPageGUIDs[i]); } } function checkForAllImagesLoaded() { for (var i = 0; i < gAllImages.length; i++) { if (!gAllImages[i].complete) { var percentage = i * 100.0 / (gAllImages.length); percentage = percentage.toFixed(0).toString() + ' %'; userMessagesController.setMessage("loading... " + percentage); setTimeout('checkForAllImagesLoaded()', 20); return; } } userMessagesController.setMessage(globals.defaultTitle); }
2

Life is too short for jquery.

function waitForImageToLoad(imageElement){ return new Promise(resolve=>{imageElement.onload = resolve}) } var myImage = document.getElementById('myImage'); var newImageSrc = "" myImage.src = newImageSrc; waitForImageToLoad(myImage).then(()=>{ // Image have loaded. console.log('Loaded lol') });
<img src="">
3

You could use the load()-event in jQuery but it won't always fire if the image is loaded from the browser cache. This plugin can be used to remedy that problem.

0

Here is jQuery equivalent:

var $img = $('img'); if ($img.length > 0 && !$img.get(0).complete) { $img.on('load', triggerAction); } function triggerAction() { alert('img has been loaded'); }

Not suitable for 2008 when the question was asked, but these days this works well for me:

async function newImageSrc(src) { // Get a reference to the image in whatever way suits. let image = document.getElementById('image-id'); // Update the source. img.src = src; // Wait for it to load. await new Promise((resolve) => { image.onload = resolve; }); // Done! console.log('image loaded! do something...'); }

If the goal is to style the img after browser has rendered image, you should:

const img = new Image(); img.src = 'path/to/img.jpg'; img.decode().then(() => { /* set styles */ /* add img to DOM */ });

because the browser first loads the compressed version of image, then decodes it, finally paints it. since there is no event for paint you should run your logic after browser has decoded the img tag.

these functions will solve the problem, you need to implement the DrawThumbnails function and have a global variable to store the images. I love to get this to work with a class object that has the ThumbnailImageArray as a member variable, but am struggling!

called as in addThumbnailImages(10);

var ThumbnailImageArray = []; function addThumbnailImages(MaxNumberOfImages) { var imgs = []; for (var i=1; i<MaxNumberOfImages; i++) { imgs.push(i+".jpeg"); } preloadimages(imgs).done(function (images){ var c=0; for(var i=0; i<images.length; i++) { if(images[i].width >0) { if(c != i) images[c] = images[i]; c++; } } images.length = c; DrawThumbnails(); }); } function preloadimages(arr) { var loadedimages=0 var postaction=function(){} var arr=(typeof arr!="object")? [arr] : arr function imageloadpost() { loadedimages++; if (loadedimages==arr.length) { postaction(ThumbnailImageArray); //call postaction and pass in newimages array as parameter } }; for (var i=0; i<arr.length; i++) { ThumbnailImageArray[i]=new Image(); ThumbnailImageArray[i].src=arr[i]; ThumbnailImageArray[i].onload=function(){ imageloadpost();}; ThumbnailImageArray[i].onerror=function(){ imageloadpost();}; } //return blank object with done() method //remember user defined callback functions to be called when images load return { done:function(f){ postaction=f || postaction } }; }
1

If you are using React.js, you could do this:

render() {

// ...

<img onLoad={() => this.onImgLoad({ item })} onError={() => this.onImgLoad({ item })} src={item.src} key={item.key} ref={item.key} />

// ... }

Where:

  • - onLoad (...) now will called with something like this: { src: "", key:"1" } you can use this as "key" to know which images is loaded correctly and which not.
  • - onError(...) it is the same but for errors.
  • - the object "item" is something like this { key:"..", src:".."} you can use to store the images' URL and key in order to use in a list of images.

    • Your Answer

    Sign up or log in

    Sign up using Google Sign up using Facebook Sign up using Email and Password

    Post as a guest

    By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy