Format number with commas and limited decimal places

Take a number like 1000.254145 and format it into a string like "1,000.25".

// adds commas and forces 2 decimal places.
function formatNumber(value, decimals) {
  let s = (+value).toLocaleString("en-US").split(".");
  return decimals
    ? s[0] + "." + ((s[1] || "") + "00000000").substr(0, decimals)
    : s[0];
}

Then you can use it in an onUpdate:

let obj = { num: 100 };
gsap.to(obj, {
  num: 10500,
  onUpdate: () => (myElement.innerText = "$" + formatNumber(obj.num, 2)),
});

getFormatter

I wasn't sure if you wanted to replace this file or create a new helper Jack? Thought as it's not urgent I would just partially do this so that you can give updating the docs a go?

function getFormatter(increment, pad) {
  let snap = gsap.utils.snap(increment),
      exp = /\B(?=(\d{3})+(?!\d))/g,
      snapWithCommas = value => (snap(+value) + "").replace(exp, ","),
      whole = increment % 1 === 0,
      decimals = whole ? 0 : ((increment + "").split(".")[1] || "0").length;
  return !pad || whole ? snapWithCommas : value => {
    let s = snapWithCommas(value),
        i = s.indexOf(".");
    ~i || (i = s.length);
    return s.substr(0, i) + "." + (s.substr(i + 1, s.length - i - 1) + "00000000").substr(0, decimals);
  };
}

let formatter = getFormatter(0.01, true); // increment by 0.01, always pad so that there are 2 decimal places

console.log(formatter(5000.1)); // 5,000.10