js method to verify image size

/**
	 * 要校验尺寸的图片元素的id，宽，高
	 */
	function checkResolution(id, width, height) {
		// 获取该图片元素
		var obj = document.getElementById(id);
		var url, image;
		// 获取元素的url源
		if (obj.files && obj.files[0]) {
			if (window.navigator.userAgent.indexOf("MSIE") >= 1) {
				obj.select();
				url = document.selection.createRange().text;
			}
			url = window.URL.createObjectURL(obj.files[0]);
		} else {
			url = obj.value;
			url = "file:///" + url;
		}
		// 构建图片
		image = new Image();
		image.src = url;
		// 加载图片
		return image.onload = function() {
			// 如果直接校验的话image.width与image.height还未赋值，所以设置延迟1ms后校验
			setTimeout(function() {
				if (image.width != width || image.height != height) {
					// 校验不通过，返回false
					alert(id + "上传的尺寸为：" + image.width + "*" + image.height
							+ ",应上传：" + width + "*" + height);
					return false;
				}
				// 校验通过，返回true
				return true;
			}, 1);
		};
	}

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