Heap's algorithm to generate the permutation of an array of n elemets

heaps-permutations.js

function permutations(s, cb){

  let n = s.length;
  function swap(i, j){
    let tmp = s[i];
    s[i] = s[j];
    s[j] = tmp;
  }

  function heapGenerate(n){
    if(n === 1){
      cb(s);
    }else{
      for(let i=0; i<n; i++){
	heapGenerate(n-1);
	if(n % 2 === 0){
	  swap(i,n-1);
	}else{
	  swap(0,n-1);
	}
      }
    }
  }
  heapGenerate(n);
}