Determining image file size + dimensions via Javascript?

As part of a web app, once images have been downloaded and rendered on a web page, I need to determine an image's file size (kb) and resolution within the browser context (so I could, for example, display that info on the page. This needs to be done client-side, obviously. Must be able to be solved x-browser without an ActiveX control or Java applet (IE7+, FF3+, Safari 3+, IE6 nice to have), though it doesn't have to be the same solution per browser.

Ideally this would be done using system Javascript, but if I absolutely need a JQuery or similar library (or a tiny subset of it), that could be done.

Edit:

To get the current in-browser pixel size of a DOM element (in your case IMG elements) excluding the border and margin, you can use the clientWidth and clientHeight properties.

var img = document.getElementById('imageId'); 

var width = img.clientWidth;
var height = img.clientHeight;

Now to get the file size, now I can only think about the fileSize property that Internet Explorer exposes for document and IMG elements...

Edit 2: Something comes to my mind...

To get the size of a file hosted on the server, you could simply make an HEAD HTTP Request using Ajax. This kind of request is used to obtain metainformation about the url implied by the request without transferring any content of it in the response.

At the end of the HTTP Request, we have access to the response HTTP Headers, including the Content-Length which represents the size of the file in bytes.

A basic example using raw XHR:

var xhr = new XMLHttpRequest();
xhr.open('HEAD', 'img/test.jpg', true);
xhr.onreadystatechange = function(){
  if ( xhr.readyState == 4 ) {
    if ( xhr.status == 200 ) {
      alert('Size in bytes: ' + xhr.getResponseHeader('Content-Length'));
    } else {
      alert('ERROR');
    }
  }
};
xhr.send(null);

Note: Keep in mind that when you do Ajax requests, you are restricted by the Same origin policy, which allows you to make requests only within the same domain.

Check a working proof of concept here.

Edit 3:

1.) About the Content-Length, I think that a size mismatch could happen for example if the server response is gzipped, you can do some tests to see if this happens on your server.

2.) For get the original dimensions of a image, you could create an IMG element programmatically, for example:

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

img.onload = function () { alert(img.width + ' x ' + img.height); };

img.src='http://sstatic.net/so/img/logo.png';

Check the uploaded image size using Javascript

<script type="text/javascript">
    function check(){
      var imgpath=document.getElementById('imgfile');
      if (!imgpath.value==""){
        var img=imgpath.files[0].size;
        var imgsize=img/1024; 
        alert(imgsize);
      }
    }
</script>

Html code

<form method="post" enctype="multipart/form-data" onsubmit="return check();">
<input type="file" name="imgfile" id="imgfile"><br><input type="submit">
</form>

Getting the Original Dimensions of the Image

If you need to get the original image dimensions (not in the browser context), clientWidth and clientHeight properties do not work since they return incorrect values if the image is stretched/shrunk via css.

To get original image dimensions, use naturalHeight and naturalWidth properties.

var img = document.getElementById('imageId'); 

var width = img.naturalWidth;
var height = img.naturalHeight;

p.s. This does not answer the original question as the accepted answer does the job. This, instead, serves like addition to it.

How about this:

var imageUrl = 'https://cdn.sstatic.net/Sites/stackoverflow/img/sprites.svg';
var blob = null;
var xhr = new XMLHttpRequest(); 
xhr.open('GET', imageUrl, true); 
xhr.responseType = 'blob';
xhr.onload = function() 
{
    blob = xhr.response;
    console.log(blob, blob.size);
}
xhr.send();

http://qnimate.com/javascript-create-file-object-from-url/

due to Same Origin Policy, only work under same origin

Regarding the width and height:

var img = document.getElementById('imageId'); 

var width = img.clientWidth;
var height = img.clientHeight;

Regarding the filesize you can use performance

var size = performance.getEntriesByName(url)[0];
console.log(size.transferSize); // or decodedBodySize might differ if compression is used on server side

Service workers have access to header informations, including the Content-Length header.

Service workers are a bit complicated to understand, so I've built a small library called sw-get-headers.

Than you need to:

1. subscribe to the library's response event
2. identify the image's url among all the network requests
3. here you go, you can read the Content-Length header!

Note that your website needs to be on HTTPS to use Service Workers, the browser needs to be compatible with Service Workers and the images must be on the same origin as your page.

Most folks have answered how a downloaded image's dimensions can be known so I'll just try to answer other part of the question - knowing downloaded image's file-size.

You can do this using resource timing api. Very specifically transferSize, encodedBodySize and decodedBodySize properties can be used for the purpose.

Check out my answer here for code snippet and more information if you seek : https://stackoverflow.com/questions/28430115/javascript-get-size-in-bytes-from-html-img-src/45409613#45409613

You can use generic Image object to load source dynamically then measure it:

    const img = new Image();
    img.src = this.getUrlSource()
    img.onload = ({target}) =>{
      let width = target.width;
      let height = target.height;
    }

You can get the dimensions using getElement(...).width and ...height.

Since JavaScript can't access anything on the local disk for security reasons, you can't examine local files. This is also true for files in the browser's cache.

You really need a server which can process AJAX requests. On that server, install a service that downloads the image and saves the data stream in a dummy output which just counts the bytes. Note that you can't always rely on the Content-length header field since the image data might be encoded. Otherwise, it would be enough to send a HTTP HEAD request.

You can find dimension of an image on the page using something like

document.getElementById('someImage').width

file size, however, you will have to use something server-side

var img = new Image();
img.src = sYourFilePath;
var iSize = img.fileSize;

The only thing you can do is to upload the image to a server and check the image size and dimension using some server side language like C#.

Edit:

Your need can't be done using javascript only.