//////// 文本框文字处理 ////////
/*
input 对象
if selectionStart=selectionEnd is point
else 是string
*/
function setSelectionRange(input, selectionStart, selectionEnd) {
  if (input.setSelectionRange) {   //firefox
    input.focus();
    input.setSelectionRange(selectionStart, selectionEnd);
  }else if (input.createTextRange) { //ie
    var range = input.createTextRange();
    range.collapse(true);
    range.moveEnd('character', selectionEnd);
    range.moveStart('character', selectionStart);
    range.select();
  }
}
function setCaretToEnd (input) {
  setSelectionRange(input, input.value.length, input.value.length);
}
function setCaretToBegin (input) {
  setSelectionRange(input, 0, 0);
}
//自定义光标插入点位置
function setCaretToPos (input, pos) {
  setSelectionRange(input, pos, pos);
}
/*光标选中对象中的string
input 对象 eg:"Visit W3School...";
string 是匹配字符串  eg: "w3school"
*/
function selectString (input, string) {
    //RegExp(string, "i")  string 不区分大小写
  var match = new RegExp(string, "i").exec(input.value);//input.value 是否匹配有string
  if (match) {
    setSelectionRange (input, match.index, match.index + match[0].length);
  }
}
//替换string
function replaceSelection (input, replaceString) {
  if (input.setSelectionRange) {
    var selectionStart = input.selectionStart;
    var selectionEnd = input.selectionEnd;
    input.value = input.value.substring(0, selectionStart)
                  + replaceString
                  + input.value.substring(selectionEnd);
    if (selectionStart != selectionEnd) // has there been a selection
      setSelectionRange(input, selectionStart, selectionStart +replaceString.length);
    else // set caret
      setCaretToPos(input, selectionStart + replaceString.length);
  }
  else if (document.selection) {
    var range = document.selection.createRange();
    if (range.parentElement() == input) {
      var isCollapsed = range.text == '';
      range.text = replaceString;
      if (!isCollapsed)  { // there has been a selection
        //it appears range.select() should select the newly
        //inserted text but that fails with IE
        range.moveStart('character', -replaceString.length);
        range.select();
      }
    }
  }
}


/**
* 文本框光标定位
**/
function setCaretPosition(elemId, caretPos) {
    var elem = document.getElementById(elemId);
    if(elem != null&&caretPos!=0) {
        if(elem.createTextRange) {
            var range = elem.createTextRange();
            range.move('character', caretPos);
            range.select();
        }
        else {
            if(elem.selectionStart) {
                elem.setSelectionRange(caretPos, caretPos);
            }
            elem.focus();
        }
        elem.scrollTop = elem.scrollHeight; 
    }
}