How to get the original size of a picture in JavaScript

Page of the IMG element, want to get its original size, take the width as an example may be the first thought is width, as follows

   
<script>   
    var img = document.getElementsByTagName (' img ') [0]   
    var width = Getwh (img, ' width ')//690   
</script>

The Getwh method used here is mentioned in the previous article. The width you get is the same as the original size of the picture.

If the IMG plus the width attribute, this way is not, for example, the actual width of the picture is 690, set a width of 400, then the way to get the above return 400

   
<script>   
    var img = document.getElementsByTagName (' img ') [0]   
    var width = Getwh (img, ' width ')/   
</script>

Obviously, 400 is not the original width of the picture.

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There is a way to get, directly create a new IMG object, and then the old img to the SRC assignment to the new, this time to get the new img width can be

   
<script>   
function Getnaturalwidth (img) {   
    var image = New Image ()   
    image.src = Img.src   
    var naturalwidth = Image.width
  return naturalwidth   
}   
var img = document.getelementsbytagname (' img ') [0]   
getnaturalwidth (IMG)//690   
</script>

It should be noted that the new image created here is not required to be added to the DOM document.

HTML5 provides a new property naturalwidth/naturalheight can directly get the original height of the picture. These two attributes have been implemented in Firefox/chrome/safari/opera and IE9. The method of obtaining picture size under transformation.

function Getimgnaturaldimensions (IMG, callback) {   
    var nwidth, nheight   
    if (img.naturalwidth) {//modern browser   
        nwidth = img.naturalwidth   
        nheight = img.naturalheight   
    } else {//IE6/7/8   
        var imgae = new Image ()   
        IMAGE.SR c = img.src   
        image.onload = function () {   
            callback (Image.width, Image.height)   
        }   
    } return   
    [nwidth , nheight]   
}

Note that the processing of IE6/7/8, created a new IMG, only set its SRC, you need to have the picture fully loaded before you can get its width and height. So here is the asynchronous, can pass a callback, the callback to the original height as a parameter passed in.