js 设置焦点到文本的最后

?? function getSelectPos(objId){
var esrc = document.getElementById(objId);
?if(esrc==null){
??? esrc=event.srcElement;
?}
?var rtextRange =esrc.createTextRange();
?rtextRange.moveStart('character',esrc.value.length);
?rtextRange.collapse(true);
?rtextRange.select();
?}