Extjs 文本框光标处插入文字

此方法对于IE 下的textfield支持不好，运行时，插入顺序错乱。

换成textarea后即可。

function insertAtCursor(myField, myValue) {
var input = document.getElementById(myField.id);
input.focus();
              if (Ext.isIE) {                 
                      sel = document.selection.createRange();
                      document.selection.empty();
                      sel.text = myValue;
              }
              else if (input.selectionStart || input.selectionStart == '0') {
             
                  var startPos = input.selectionStart;
                  var endPos = input.selectionEnd;
                  input.value = input.value.substring(0, startPos)
                              + myValue
                              + input.value.substring(endPos, input.value.length);
              } else {
              input.value += myValue;
              }
        }