js 光标位置处理

  /**
   * 获取选中文字
   * 返回selection,toString可拿到结果,selection含有起始光标位置信息等
   **/
  function getSelectText() {
      var text,
          userSelection = window.getSelection()||document.selection.createRange();// not IE || ie
      if (!(text = userSelection.text)) text = userSelection;

      return text;
  }
  /**
   * 获取光标位置
   * 对 input、textarea有效，对contenteditable:true方式不生效
   **/
  function getCursortPosition (textDom) {
    var cursorPos = 0;
    if (document.selection) {
        // IE Support
        textDom.focus ();
        var selectRange = document.selection.createRange();
        selectRange.moveStart ('character', -textDom.value.length);
        cursorPos = selectRange.text.length;
    }else if (textDom.selectionStart || textDom.selectionStart == '0') {
        // 非 IE
        cursorPos = textDom.selectionStart;
    }
    return cursorPos;
  }
  /**
   * 设置光标位置
   * 有效对象同光标获取
   **/
  function setCaretPosition(textDom, pos){
      if(textDom.setSelectionRange) {
          // IE Support
          textDom.focus();
          textDom.setSelectionRange(pos, pos);
      }else if (textDom.createTextRange) {
          // 非 IE
          var range = textDom.createTextRange();
          range.collapse(true);
          range.moveEnd('character', pos);
          range.moveStart('character', pos);
          range.select();
      }
  }