javascript获取以及设置光标位置

// 获取光标位置
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') {
  // Firefox support
  cursorPos = textDom.selectionStart;
 }
 return cursorPos;
}

// 设置光标位置
function setCaretPosition(textDom, pos){
 if(textDom.setSelectionRange) {
  // IE Support
  textDom.focus();
  textDom.setSelectionRange(pos, pos);
 }else if (textDom.createTextRange) {
  // Firefox support
  var range = textDom.createTextRange();
  range.collapse(true);
  range.moveEnd('character', pos);
  range.moveStart('character', pos);
  range.select();
 }
}

// 获取选中文字
function getSelectText() {
 var userSelection, text;
 if (window.getSelection) {
  // Firefox support
  userSelection = window.getSelection();
 } else if (document.selection) {
  // IE Support
  userSelection = document.selection.createRange();
 }
 if (!(text = userSelection.text)) {
  text = userSelection;
 }
 return text;
}

/**
* 选中特定范围的文本
* 参数：
*  textDom [JavaScript DOM String] 当前对象
*  startPos [Int] 起始位置
*  endPos [Int] 终点位置
*/
function setSelectText(textDom, startPos, endPos) {
 var startPos = parseInt(startPos),
  endPos = parseInt(endPos),
  textLength = textDom.value.length;
 if(textLength){
  if(!startPos){
   startPos = 0;
  }
  if(!endPos){
   endPos = textLength;
  }
  if(startPos > textLength){
   startPos = textLength;
  }
  if(endPos > textLength){
   endPos = textLength;
  }
  if(startPos < 0){
   startPos = textLength + startPos;
  }
  if(endPos < 0){
   endPos = textLength + endPos;
  }
  if(textDom.createTextRange){
   // IE Support
   var range = textDom.createTextRange();
   range.moveStart("character",-textLength);
   range.moveEnd("character",-textLength);
   range.moveStart("character", startPos);
   range.moveEnd("character",endPos);
   range.select();
  }else{
   // Firefox support
   textDom.setSelectionRange(startPos, endPos);
   textDom.focus();
  }
 }
}

/**
* 在光标后插入文本
* 参数：
*  textDom [JavaScript DOM String] 当前对象
*  value [String] 要插入的文本
*/
function insertAfterText(textDom, value) {
 var selectRange;
 if (document.selection) {
  // IE Support
  textDom.focus();
  selectRange = document.selection.createRange();
  selectRange.text = value;
  textDom.focus();
 }else if (textDom.selectionStart || textDom.selectionStart == '0') {
  // Firefox support
  var startPos = textDom.selectionStart;
  var endPos = textDom.selectionEnd;
  var scrollTop = textDom.scrollTop;
  textDom.value = textDom.value.substring(0, startPos) + value + textDom.value.substring(endPos, textDom.value.length);
  textDom.focus();
  textDom.selectionStart = startPos + value.length;
  textDom.selectionEnd = startPos + value.length;
  textDom.scrollTop = scrollTop;
 }
 else {
  textDom.value += value;
  textDom.focus();
 }
}