Prime Number Utilities

prime.js

var number = {
  primes: [],
  computeSieve: function(max) {
    var composites = [], primes = [];

    for ( var composite = 2; composite < max; composite++ ) {
      this.computeComposite(primes, composites, composite, max);
    }

    return primes;
  },
  computeComposite: function(primes, composites, composite, max) {
    var currentComposite = composites[composite];

    if ( currentComposite) {
      for ( var i = 0; i < currentComposite.length; i++ ) {
        var potentialPrime = currentComposite[i];
        var newComposite = ( potentialPrime + composite );

        if ( composites[newComposite] ) {
          composites[newComposite].push(potentialPrime);
        } else {
          composites[newComposite] = [potentialPrime];
        }
      }

      delete composites[composite];
    } else {
      primes.push(composite);

      var newComposite = ( composite * composite );

      if ( !max || newComposite < max ) {
        composites[newComposite] = [composite];
      }

    }
  },
  generateToAmount: function(amount) {
    var composites = [], primes = [], composite = 2;

    while ( primes.length < amount ) {
      this.computeComposite(primes, composites, composite);
      composite++;
    }

    return primes;
  },
  containsNumber: function(number) {
    return this.primes.indexOf(number) !== -1;
  },
  isPrime: function(number) {
    if ( number == 2 || number == 3 )
      return true;

    if ( this.primes.length <= 0 || !this.containsNumber(number)) {
      this.primes = this.computeSieve(number + 1);
    }

    return this.containsNumber(number);
  },
  generatePrimes: function(amount) {
    if ( this.primes.length >= amount )
      return this.primes.slice(0, amount - 1);

    this.primes = this.generateToAmount(amount);

    return this.primes;
  }
};

var command = process.argv[2];
var arg = parseInt(process.argv[3]);

if ( !command || !arg ) {
  console.log('usage: node prime.js [/g amount] [/c number]');
  return;
}

switch ( command ) {
  case '/c':
    console.log('Checking if ' + arg + ' is a prime number');
    console.log(number.isPrime(arg));
    break;
  case '/g':
    console.log('Generating ' + arg + ' prime numbers');
    console.log(number.generatePrimes(arg));
    break;
}