function insertAtCursor(myField, myValue) {   //IE 瀏覽器  if (document.selection) {   myField.focus();   sel = document.selection.createRange();   sel.text = myValue;   sel.select();  }   //FireFox、Chrome等  else if (myField.selectionStart || myField.selectionStart == '0') {   var startPos = myField.selectionStart;   var endPos = myField.selectionEnd;    // 保存滾動條   var restoreTop = myField.scrollTop;   myField.value = myField.value.substring(0, startPos) + myValue + myField.value.substring(endPos, myField.value.length);     if (restoreTop > 0) {   myField.scrollTop = restoreTop;   }     myField.focus();   myField.selectionStart = startPos + myValue.length;   myField.selectionEnd = startPos + myValue.length;  } else {   myField.value += myValue;   myField.focus();  } } <textarea id="textarea" style="width: 386px; height: 260px"> </textarea> <input type="text" id="text" /> <input type="button" value="插入" onclick="insertAtCursor(document.getElementById('textarea'),document.getElementById('text').value)" />