JS实现的图片预览功能

<table width="100%" border="0" cellspacing="0" cellpadding="0">
			<tbody>
				<tr>
					<td height="101" align="center">
						<div id="localImag"><img id="preview" src="http://blog.chuangling.net/Public/images/top.jpg" width="150" height="180" style="display: block; width: 150px; height: 180px;"></div>
					</td>
				</tr>
				<tr>
					<td align="center" style="padding-top:10px;"><input type="file" name="file" id="doc" style="width:150px;" onchange="javascript:setImagePreview();"></td>
				</tr>
			</tbody>
		</table>

function setImagePreview(avalue) {
				var docObj = document.getElementById("doc");
				var imgObjPreview = document.getElementById("preview");
				if(docObj.files && docObj.files[0]) 
				{ 
					//火狐下，直接设img属性
					imgObjPreview.style.display = ‘block‘;
					imgObjPreview.style.width = ‘150px‘;
					imgObjPreview.style.height = ‘180px‘;
					//imgObjPreview.src = docObj.files[0].getAsDataURL(); 
					//火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式
					imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
				} 
				else 
				{
					//IE下，使用滤镜
					docObj.select();
					var imgSrc = document.selection.createRange().text;
					var localImagId = document.getElementById("localImag"); //必须设置初始大小
					localImagId.style.width = "150px";
					localImagId.style.height = "180px"; //图片异常的捕捉，防止用户修改后缀来伪造图片
					try {
						localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
						localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
					} catch(e) {
						alert("您上传的图片格式不正确，请重新选择!");
						return false;
					}
					imgObjPreview.style.display = ‘none‘;
					document.selection.empty();
				}
				return true;
			}