JS - get image width and height from the base64 code

I have a base64 img encoded that you can find here. How can I get the height and the width of it?

var i = new Image(); 

i.onload = function(){
 alert( i.width+", "+i.height );
};

i.src = imageData; 

For synchronous use just wrap it into a promise like this:

function getImageDimensions(file) {
  return new Promise (function (resolved, rejected) {
    var i = new Image()
    i.onload = function(){
      resolved({w: i.width, h: i.height})
    };
    i.src = file
  })
}

then you can use await to get the data in synchronous coding style:

var dimensions = await getImageDimensions(file)

I found that using .naturalWidth and .naturalHeight had the best results.

const img = new Image();

img.src = 'https://via.placeholder.com/350x150';

img.onload = function() {
  const imgWidth = img.naturalWidth;
  const imgHeight = img.naturalHeight;

  console.log('imgWidth: ', imgWidth);
  console.log('imgHeight: ', imgHeight);
};

Docs:

• https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/naturalWidth
• https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/naturalHeight

This is only supported in modern browsers. http://www.jacklmoore.com/notes/naturalwidth-and-naturalheight-in-ie/

Create a hidden <img> with that image and then use jquery .width() and . height()

$("body").append("<img id='hiddenImage' src='"+imageData+"' />");
var width = $('#hiddenImage').width();
var height = $('#hiddenImage').height();
$('#hiddenImage').remove();
alert("width:"+width+" height:"+height);

Test here: FIDDLE

Image is not initially created hidden. it gets created, then you get width and height and then remove it. This may cause a very short visibility in large images in this case you have to wrap the image in another container and make that container hidden not the image itself.

---

Another Fiddle that does not add to dom as per gp.'s anser : HERE

A more modern solution is to use decode() instead of the onload event. decode() returns a promise, thus can be used synchronously with await.

Asynchronous use:

let img = new Image();
img.src = "myImage.png";
img.decode().then(() => {
    let width = img.width;
    let height = img.height;
    // Do something with dimensions
});

Synchronous use (inside async function):

let img = new Image();
img.src = "myImage.png";
await img.decode();
let width = img.width;
let height = img.height;
// Do something with dimensions