power.js

function power(x , y) {
  var base = x;
  if ( y < 0 ) {
    base = 1 / x;
    y = -1*y;
  }
  var coeff = 1;
  while (y > 1) {
    if (y%2 == 0) {
      base *= base;
      y = Math.floor(y / 2);
    }
    else {
      coeff *= base;
      base *= base;
      y = Math.floor((y - 1) / 2);
    }
  }
  return coeff * base
}