js 中英文字符串取出中文字符

var a = "你们还是too simple";
var b = "";
for (var i = 0; i < a.length; i++) {
    if (a.charCodeAt(i) > 256 && a[i] != " ") {
        b += a[i];
    } else {
        break;
    }
}
console.log(b);  //"你们还是"