textarea光标定位问题

 

在项目中解决textarea光标定位问题，让光标定位在内容里面或内容后面
function savePos(textBox){

 //如果是Firefox(1.5)的话，方法很简单
 if(typeof(textBox.selectionStart) == "number"){
  start = textBox.selectionStart;
  end = textBox.selectionEnd;
 }
 //下面是IE(6.0)的方法，麻烦得很，还要计算上'\n'
 else if(document.selection){
  var range = document.selection.createRange();
  if(range.parentElement().id == textBox.id){
 // create a selection of the whole textarea
  var range_all = document.body.createTextRange();
  range_all.moveToElementText(textBox);
 //两个range，一个是已经选择的text(range)，一个是整个textarea(range_all)
 //range_all.compareEndPoints()比较两个端点，如果range_all比range更往左(further to the left)，则 //返回小于0的值，则range_all往右移一点，直到两个range的start相同。
 // calculate selection start point by moving beginning of range_all to beginning of range
 for (start=0; range_all.compareEndPoints("StartToStart", range) < 0; start++)
  range_all.moveStart('character', 1);
 // get number of line breaks from textarea start to selection start and add them to start
 // 计算一下\n
 for (var i = 0; i <= start; i ++){
  if (textBox.value.charAt(i) == '\n')
   start++;
 }
 // create a selection of the whole textarea
 var range_all = document.body.createTextRange();
 range_all.moveToElementText(textBox);
 // calculate selection end point by moving beginning of range_all to end of range
 for (end = 0; range_all.compareEndPoints('StartToEnd', range) < 0; end ++)
  range_all.moveStart('character', 1);
 // get number of line breaks from textarea start to selection end and add them to end
 for (var i = 0; i <= end; i ++){
  if (textBox.value.charAt(i) == '\n')
 end ++;
 }
 }
 }

}

     οnmοusedοwn="savePos(this)" οnmοuseup="savePos(this)" οnfοcus="savePos(this)">