JS截取字符串方法

function textSubstr(str,sub_length){
    str = str.trim();
    var temp1 = str.replace(/[^x00-xff]/g,"**");//精髓
    var mlength = 22;
    if(sub_length == undefined){
        var temp2 = temp1.substring(0,mlength);
        //找出有多少个*
        var x_length = temp2.split("*").length - 1 ;
        var hanzi_num = x_length /2 ;
        var sub_length = mlength - hanzi_num ;//实际需要sub的长度是总长度-汉字长度
        var res = str.substring(0,sub_length);            
    }else{
        var temp2 = temp1.substring(0,sub_length);
        //找出有多少个*
        var x_length = temp2.split("*").length - 1 ;
        var hanzi_num = x_length /2 ;
        var sub_length = sub_length - hanzi_num ;//实际需要sub的长度是总长度-汉字长度
        var res = str.substring(0,sub_length);        
    }
    if(sub_length < str.length){
       var end =res+"...";
    }else{
       var end = res;
    }
    return end;
}

字数超过部分用。。。省略