function makeIndex(a, b) {
  let index = Object.create(null);

  ((a || []).concat(b ||[])).forEach(function(a) {
    index[a] = true;
  });

  return index;
}
// Pulled straight from broccoli-concat :(
Pulled straight from broccoli-concat :(
Pulled straight from broccoli - concat : (
function makeIndex(a, b) {
  let index = Object.create(null);
  ((a || []).concat(b ||[])).forEach(function(a) {
    index[a] = true;
  });
  return index;
}
function makeIndex ( a , b ) { let index = Object . create ( null ) ; ( ( a || [ ] ) . concat ( b || [ ] ) ) . forEach ( function ( a ) { index [ a ] = true ; } ) ; return index ; }
Pulled straight from broccoli-concat :(
Pulled straight from broccoli - concat : (