js方法格式化数字，加入千分符，并可以指定小数点位数，支持负数

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//js方法格式化数字，加入千分符，并可以指定小数点位数
function number(s, n) {
  n = n >= 0 && n <= 20 ? n : 2;
  s = parseFloat((s + "").replace(/[^\d\.-]/g, "")).toFixed(n) + "";
  var l = s
    .split(".")[0]
    .split("")
    .reverse(),
    r = s.split(".")[1];
  r = r == null ? "" : "." + r;
  var t = "";
  console.log(l)
  if (l[l.length - 1] === '-') {//负数不需要分隔号,

    for (var i = 0; i < l.length; i++) {
      if (l[i]==='-') {
        t += l[i]+""
        continue
      }
      //不是数组的倒数第二个元素才加"," ["0", "4", "5", "-"]
      t += l[i] + ((i + 1) % 3 == 0 && i + 1 != l.length-1 ? "," : "");

      //i + 1 != l.length会变成-,540.00,因为在5时元素位置2+1为3非数组长度
      //t += l[i] + ((i + 1) % 3 == 0 && i + 1 != l.length ? "," : "");
    }
  }
  else {
    for (var i = 0; i < l.length; i++) {
      t += l[i] + ((i + 1) % 3 == 0 && i + 1 != l.length ? "," : "");
    }
  }
  return (
    t
      .split("")
      .reverse()
      .join("") + r
  );
}