超出的字符长度截取显示省略号(...) 按字节长度计算

function num(str,len){
    var result = ""; 
    var count = 0;
    for (var i = 0; i < len; i++) { 
    var _char = str.charAt(i); 
    if (count >= len) break; 
    if (/[^x00-xff]/.test(_char)) count++; //双字节字符，//[u4e00-u9fa5]中文

    result += _char; 
    count++; 
    } 
    if (result.length < str.length) { 
    result += "..."; 
        console.log(result)
    }else{
        console.log(result)
    }
}