Detect when an image fails to load in Javascript

113

Is there a way to determine if a image path leads to an actual image, Ie, detect when an image fails to load in Javascript.

For a web app, I am parsing a xml file and dynamically creating HTML images from a list of image paths. Some image paths may no longer exist on the server so I want to fail gracefully by detecting which images fail to load and deleting that HTML img element.

Note JQuery solutions wont be able to be used(the boss doesn't want to use JQuery, yes I know dont get me started). I know of a way in JQuery to detect when an image is loaded, but not whether it failed.

My code to create img elements but how can I detect if the img path leads to a failed to load image?

var imgObj = new Image();  // document.createElement("img");
imgObj.src = src;

This question is tagged with javascript image

~ Asked on 2012-03-22 02:50:43

The Best Answer is


121

You could try the following code. I can't vouch for browser compatibility though, so you'll have to test that.

function testImage(URL) {
    var tester=new Image();
    tester.onload=imageFound;
    tester.onerror=imageNotFound;
    tester.src=URL;
}

function imageFound() {
    alert('That image is found and loaded');
}

function imageNotFound() {
    alert('That image was not found.');
}

testImage("http://foo.com/bar.jpg");

And my sympathies for the jQuery-resistant boss!

~ Answered on 2012-03-22 03:03:18


53

The answer is nice, but it introduces one problem. Whenever you assign onload or onerror directly, it may replace the callback that was assigned earlier. That is why there's a nice method that "registers the specified listener on the EventTarget it's called on" as they say on MDN. You can register as many listeners as you want on the same event.

Let me rewrite the answer a little bit.

function testImage(url) {
    var tester = new Image();
    tester.addEventListener('load', imageFound);
    tester.addEventListener('error', imageNotFound);
    tester.src = url;
}

function imageFound() {
    alert('That image is found and loaded');
}

function imageNotFound() {
    alert('That image was not found.');
}

testImage("http://foo.com/bar.jpg");

Because the external resource loading process is asynchronous, it would be even nicer to use modern JavaScript with promises, such as the following.

function testImage(url) {

    // Define the promise
    const imgPromise = new Promise(function imgPromise(resolve, reject) {

        // Create the image
        const imgElement = new Image();

        // When image is loaded, resolve the promise
        imgElement.addEventListener('load', function imgOnLoad() {
            resolve(this);
        });

        // When there's an error during load, reject the promise
        imgElement.addEventListener('error', function imgOnError() {
            reject();
        })

        // Assign URL
        imgElement.src = url;

    });

    return imgPromise;
}

testImage("http://foo.com/bar.jpg").then(

    function fulfilled(img) {
        console.log('That image is found and loaded', img);
    },

    function rejected() {
        console.log('That image was not found');
    }

);

~ Answered on 2016-09-19 13:24:45


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