algorithms.js

function primes(num){
  var result = [2, 3];
  for(var i = 5; i<= num; i+=2){
    if ( result.every( x => i % x ) ) {
      result.push(i);
    }    
  }  
  return result;
}

function gcdArr(arr){
  return arr.reduce((prev, curr) => gcd(prev, curr));
}

function gcd(a, b) {
  var t;
   while (b !== 0) {
       t = b; 
       b = a % b; 
       a = t; 
   }
   return a;
}

function lcm(a, b){
  return a * b / gcd(a, b);
}

function getRotations(x){
    var result = [];
    x = x.toString().split('');
    for(var i=0; i< x.length-1; i++){
        // rotate
        x.unshift(x.pop());
        result.push(x.join(''));
    }
    return result;
}

function formatNumber(x){
    // Matches a zero-width non-word boundary, such as between two letters or between two spaces.
    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp

    //return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
    return x.toString().replace(/(\d)(?=(\d{3})+(?!\d))/g, "$1,");
}