JS复制对应id的内容到粘贴板（Ctrl+C效果）

<tr>
 <td>
 <a id="copy_{$key}" onclick="getUrl('{$key}')">复制文件链接</a>
 <input id="file_{$key}" value="{$file.file_url}" style="margin-left: -9999px"/>
 </td>
</tr> 

<pre><script type="application/javascript">
 
 function getUrl(id) {
  if (copyToClipboard(document.getElementById("file_"+id))){
   alert("成功复制到黏贴板！");
  }else{
   alert("复制到黏贴板失败！");
  }
 }
 
 function copyToClipboard(elem) {
  // create hidden text element, if it doesn't already exist
  var targetId = "_hiddenCopyText_";
  var isInput = elem.tagName === "INPUT" || elem.tagName === "TEXTAREA";
  var origSelectionStart, origSelectionEnd;
  if (isInput) {
   // can just use the original source element for the selection and copy
   target = elem;
   origSelectionStart = elem.selectionStart;
   origSelectionEnd = elem.selectionEnd;
  } else {
   // must use a temporary form element for the selection and copy
   target = document.getElementById(targetId);
   if (!target) {
    var target = document.createElement("textarea");
    target.style.position = "absolute";
    target.style.left = "-9999px";
    target.style.top = "0";
    target.id = targetId;
    document.body.appendChild(target);
   }
   target.textContent = elem.textContent;
  }
  // select the content
  var currentFocus = document.activeElement;
  target.focus();
  target.setSelectionRange(0, target.value.length);
 
  // copy the selection
  var succeed;
  try {
   succeed = document.execCommand("copy");
  } catch(e) {
   succeed = false;
  }
  // restore original focus
  if (currentFocus && typeof currentFocus.focus === "function") {
   currentFocus.focus();
  }
 
  if (isInput) {
   // restore prior selection
   elem.setSelectionRange(origSelectionStart, origSelectionEnd);
  } else {
   // clear temporary content
   target.textContent = "";
  }
  return succeed;
 }
</script></pre>