image.onError event never fires, but image isn'

问题:

I am trying to append an image to a page using JavaScript:

image = document.createElement('img');
image.onload = function(){
    document.body.appendChild(image);
}
image.onerror = function(){
    //display error
}
image.src = 'http://example.com/image.png';

The user must be authenticated to see this image, and if they are not, I want to display an error message. Unfortunately, the server is not returning an HTTP error message, but rather redirect the request to a (mostly) empty page, so I am getting an HTTP 200, but the warning Resource interpreted as Image but transferred with MIME type text/html and nothing is displaying.

How can I handle this case? I don't have the ability to change what the webserver serves up if the user isn't authenticated.

回答1:

In the image.onload event listener, check whether image.width and image.height are both zero (preferably image.naturalWidth and image.naturalHeight, when they are supported).

If the width and height are both zero, the image is considered invalid.

Demo: http://jsfiddle.net/RbNeG/

// Usage:
loadImage('notexist.png');

function loadImage(src) {
    var image = new Image;
    image.onload = function() {
        if ('naturalHeight' in this) {
            if (this.naturalHeight + this.naturalWidth === 0) {
                this.onerror();
                return;
            }
        } else if (this.width + this.height == 0) {
            this.onerror();
            return;
        }
        // At this point, there's no error.
        document.body.appendChild(image);
    };
    image.onerror = function() {
        //display error
        document.body.appendChild(
            document.createTextNode('\nError loading as image: ' + this.src)
        );
    };
    image.src = src;
}

回答2:

Here is my solution. If I've 404 for my image - I try to insert one of my array that is 200 OK (Pure Javascript). Images must be in same path. Otherwise - my func will return 'no-image.png'. jQuery/JavaScript to replace broken images