How do you print numbers with commas as thousand separators

You can use the Number.prototype.toLocaleString() method which returns a string with a language-sensitive representation such as thousand separator, currency etc. of this number.

  function convertToThousandFormat(x) {
    return x.toLocaleString(); // 12,345.679
  }

  console.log(convertToThousandFormat(12345.6789));