sheetjs-clone/packages/ssf/bits/56_commaify.js

function commaify(s/*:string*/)/*:string*/ {
	var w = 3;
	if(s.length <= w) return s;
	var j = (s.length % w), o = s.substr(0,j);
	for(; j!=s.length; j+=w) o+=(o.length > 0 ? "," : "") + s.substr(j,w);
	return o;
}