clientWidth 和 clientHeight 是DOM属性，显示DOM元素内部维度的当前浏览器内大小（不包括边距和边框）。因此，对于IMG元素，这将获得可见图像的实际尺寸。

clientWidth and clientHeight are DOM properties that show the current in-browser size of the inner dimensions of a DOM element (excluding margin and border). So in the case of an IMG element, this will get the actual dimensions of the visible image.

var img = document.getElementById('imageid'); 
//or however you get a handle to the IMG
var width = img.clientWidth;
var height = img.clientHeight;