Combinations of string characters all unique

comb.js

var combinations = function(str) {
  var arr = str.split('');
  for( var i=0; i< arr.length; i++){
      genComb(arr, i+1); 
  }
}

function genComb(arr, length, str, index) { 
  str = str || '';
  index = index || 0;
  if(str.length === length) {
      console.log(str, length); 
      return;
     }
  
  for(i=index; i<arr.length; i++){
    genLenPermu(arr, length, str+arr[i], i+1); 
  }
}

combinations('aaa');