设置contenteditable的非表单元素限制字数时设置光标位置

html:
请输入选项内容

js:
$("#optionA").on({  
      input:function(e){
             limited(e.target.id,30);
        },
        click:function(e){
            write($("#"+e.target.id));
        }           
});
//字符串截取
function limited(obj,num){
     var commentLength=$('#'+obj).text().length;
     if(commentLength>num){
        $('#'+obj).html($('#'+obj).text().substring(0,num)).attr('data-val',$('#'+obj).text().substring(0,num));
     }else{
         $('#'+obj).html($('#'+obj).text()).attr('data-val',$('#'+obj).text());   
     }
     set_focus(obj);
}
//光标置于文字末端
function set_focus(ele){
    var el=document.getElementById(ele);
    el.focus();
    if($.support.msie){
        var range = document.selection.createRange();
        this.last = range;
        range.moveToElementText(el);
        range.select();
        document.selection.empty(); //取消选中
    }else{
        var range = document.createRange();
        range.selectNodeContents(el);
        range.collapse(false);
        var sel = window.getSelection();
        sel.removeAllRanges();
        sel.addRange(range);
    }
}