parseDuration.js

var re = /([\d.]+)(s|ms)?/, units = {ms: 1, s: 1e3};
var parseDuration = function(value){
	var match = value.toString().match(re);
	return match ? parseFloat(match[1]) * (units[match[2]] || 1) : parseFloat(value)
};

console.log(parseDuration(200));
console.log(parseDuration('200'));
console.log(parseDuration('200ms'));
console.log(parseDuration('.2s'));