使用 JavaScript 下载图像

Question

Right now I have a canvas and I want to save it as PNG. I can do it with all those fancy complicated file system API, but I don't really like them.

I know if there is a link with download attribute on it:

<a href="img.png" download="output.png">Download</a>

it will download the file if the user clicks on it. Therefore I came up with this:

$("<a>")
    .attr("href", "img.png")
    .attr("download", "output.png")
    .appendTo("body")
    .click()
    .remove();

Demo: http://jsfiddle.net/DerekL/Wx7wn/

However, it doesn't seem to work. Does it have to be trigger by an user action? Or else why didn't it work?

Answer 1

The problem is that jQuery doesn't trigger the native click event for <a> elements so that navigation doesn't happen (the normal behavior of an <a> ), so you need to do that manually. For almost all other scenarios, the native DOM event is triggered (at least attempted to - it's in a try/catch).

To trigger it manually, try:

var a = $("<a>")
    .attr("href", "http://i.stack.imgur.com/L8rHf.png")
    .attr("download", "img.png")
    .appendTo("body");

a[0].click();

a.remove();

DEMO: http://jsfiddle.net/HTggQ/

Relevant line in current jQuery source: https://github.com/jquery/jquery/blob/1.11.1/src/event.js#L332

if ( (!special._default || special._default.apply( eventPath.pop(), data ) === false) &&
        jQuery.acceptData( elem ) ) {

Answer 2

As @Ian explained , the problem is that jQuery's click() is not the same as the native one.

Therefore, consider using vanilla-js instead of jQuery:

var a = document.createElement('a');
a.href = "img.png";
a.download = "output.png";
document.body.appendChild(a);
a.click();
document.body.removeChild(a);

Demo