Tobias Lütke Tobias Lütke - 4 years ago 114
Javascript Question

Detecting an image 404 in javascript

After a user uploads a file we have to do some additional processing with the images such as resizing and upload to S3. This can take up to 10 extra seconds. Obviously we do this in a background. However, we want to show the user the result page immediately and simply show spinners in place until the images arrive in their permanent home on s3.

I'm looking for a way to detect that a certain image failed to load correctly (404) in a cross browser way. If that happens, we want to use JS to show a spinner in it's place and reload the image every few seconds until it can be successfully loaded from s3.

Answer Source

From: http://lucassmith.name/2008/11/is-my-image-loaded.html

// First a couple helper functions
function $(id) {
    return !id || id.nodeType === 1 ? id : document.getElementById(id);
}
function isType(o,t) {    return (typeof o).indexOf(t.charAt(0).toLowerCase()) === 0;}

// Here's the meat and potatoes
function image(src,cfg) {    var img, prop, target;
    cfg = cfg || (isType(src,'o') ? src : {});

    img = $(src);
    if (img) {
        src = cfg.src || img.src;
    } else {
        img = document.createElement('img');
        src = src || cfg.src;
    }

    if (!src) {
        return null;
    }

    prop = isType(img.naturalWidth,'u') ? 'width' : 'naturalWidth';
    img.alt = cfg.alt || img.alt;

    // Add the image and insert if requested (must be on DOM to load or
    // pull from cache)
    img.src = src;

    target = $(cfg.target);
    if (target) {
        target.insertBefore(img, $(cfg.insertBefore) || null);
    }

    // Loaded?
    if (img.complete) {
        if (img[prop]) {
            if (isType(cfg.success,'f')) {
                cfg.success.call(img);
            }
        } else {
            if (isType(cfg.failure,'f')) {
                cfg.failure.call(img);
            }
        }
    } else {
        if (isType(cfg.success,'f')) {
            img.onload = cfg.success;
        }
        if (isType(cfg.failure,'f')) {
            img.onerror = cfg.failure;
        }
    }

    return img;
}

And here how to use it:

image('imgId',{
    success : function () { alert(this.width); },
    failure : function () { alert('Damn your eyes!'); },
});

image('http://somedomain.com/image/typooed_url.jpg', {
    success : function () {...},
    failure : function () {...},
    target : 'myContainerId',
    insertBefore : 'someChildOfmyContainerId'
});
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