function format_number(n) {    n = n + '';    var re = /^-?[0-9]+.?[0-9]*$/;    if (!re.test(n)) {        return n;    }    var pos = n.indexOf(".");    var part1;    var part2;    if (pos > -1) {        part1 = n.substr(0, pos);        part2 = n.substr(pos + 1);    } else {        part1 = n;    }    var sign = '';    if (part1.indexOf('-') > -1) {        sign = part1.slice(0, 1);        part1 = part1.slice(1);    }    var len = part1.length;    if (len > 3) {        var r = len % 3;        part1 = r > 0 ? part1.slice(0, r) + "," + part1.slice(r, len).match(/\d{3}/g).join(",") : part1.slice(r, len).match(/\d{3}/g).join(",");    }    if (part2) {        return sign + part1 + '.' + part2;    } else {        return sign + part1;    }};

效果如下；

1234.01 ⇒1,234.01

-1234.01 ⇒-1,234.01