div中获取一段文字后面的焦点

function myfocus(obj) {    if (typeof obj == 'string') obj = document.getElementById(obj);    obj.focus();    if (obj.createTextRange) {//ie        var rtextRange = obj.createTextRange();        if(obj.value == null || obj.value == '') return;        rtextRange.moveStart('character', obj.value.length);        rtextRange.collapse(true);        rtextRange.select();    }else if (obj.selectionStart){//chrome "<input>"、"<textarea>"        obj.selectionStart = obj.value.length;    }else if(window.getSelection){    var sel = window.getSelection();                var tempRange = document.createRange();    if(obj.firstChild == null || obj.firstChild == '') return;    tempRange.setStart(obj.firstChild, obj.firstChild.length);    sel.removeAllRanges();    sel.addRange(tempRange);}}