Get image dimensions with Javascript before image has fully loaded

问题

I've read about various kinds of ways getting image dimensions once an image has fully loaded, but would it be possible to get the dimensions of any image once it just started to load?

I haven't found much about this by searching (which makes me believe it's not possible), but the fact that a browser (in my case Firefox) shows the dimensions of any image I open up in a new tab right in the title after it just started loading the image gives me hope that there actually is a way and I just missed the right keywords to find it.

回答1:

You are right that one can get image dimensions before it's fully loaded.

Here's a solution (demo):

var img = document.createElement('img');

img.src = 'some-image.jpg';

var poll = setInterval(function () {
    if (img.naturalWidth) {
        clearInterval(poll);
        console.log(img.naturalWidth, img.naturalHeight);
    }
}, 10);

img.onload = function () { console.log('Fully loaded'); }

回答2:

The following code returns width/height as soon as it's available. For testing change abc123 in image source to any random string to prevent caching.

There is a JSFiddle Demo as well.

<div id="info"></div>
<img id="image" src="https://upload.wikimedia.org/wikipedia/commons/d/da/Island_Archway,_Great_Ocean_Rd,_Victoria,_Australia_-_Nov_08.jpg?abc123">

<script>
getImageSize($('#image'), function(width, height) {
    $('#info').text(width + ',' + height);
});

function getImageSize(img, callback) {
    var $img = $(img);

    var wait = setInterval(function() {
        var w = $img[0].naturalWidth,
            h = $img[0].naturalHeight;
        if (w && h) {
            clearInterval(wait);
            callback.apply(this, [w, h]);
        }
    }, 30);
}
</script>

回答3:

One way is to use the HEAD request, which asks for HTTP Header of the response only. I know in HEAD responses, the size of the body is included. But I don't know if there anything available for size of images.

回答4:

Actually it's a lot easier, you just have to fetch the dimensions in the image's onload function.

var tempImage1 = new Image();
tempImage1.src = "path/to/image";
tempImage1.onload = function() {
    console.log(tempImage1.width, tempImage1.height);
}

来源：https://stackoverflow.com/questions/6575159/get-image-dimensions-with-javascript-before-image-has-fully-loaded

标签

javascript

image

dimensions