numPrimes.js

var M = 100000;
var st = Date.now();
console.log(numPrimes1(M));
console.log((Date.now() - st)+" msec");

var st = Date.now();
console.log(numPrimes2(M));
console.log((Date.now() - st)+" msec");

function numPrimes1(max) {
	var num = 0;
	for (var i = 2; i <= max; i ++) {
		if (isPrime(i)) num += 1;
	}
	return num;
	function isPrime(x) {
		var m = Math.floor(x / 2);
		if (x == 1) return false;
		for (var i = 2; i <= m; i ++) {
			if (Math.floor(x / i) * i == x) return false;
		}
		return true;
	}
}
function numPrimes2(max) {
	var floor = Math.floor;
	var num = 0;
	for (var i = 2; i <= max; i ++) {
		if (isPrime(i)) num += 1;
	}
	return num;
	function isPrime(x) {
		var m = floor(x / 2);
		if (x == 1) return false;
		for (var i = 2; i <= m; i ++) {
			if (floor(x / i) * i == x) return false;
		}
		return true;
	}
}