<form name="form5" id="form5" method="post" action="#"> <input type="file" name="file5" id="file5" onchange="preview5()"/> </form> <script type="text/javascript"> function preview5(){ var x = document.getElementById("file5");  if(!x || !x.value) return; var patn = /\.jpg$|\.jpeg$|\.gif$/i; if(patn.test(x.value)){  var y = document.getElementById("img5"); if(y){ y.src = "file://localhost/" + x.value; }else{ var img=document.createElement("img");      img.setAttribute("src","file://localhost/"+x.value); img.setAttribute("width","120"); img.setAttribute("height","90"); img.setAttribute("id","img5"); document.getElementById("form5").appendChild(img);  } }else{ alert("您选择的似乎不是图像文件。"); }} </script>