code: function diff( a, b ) {
    let i, j, found = false, result = [];
  
    for ( i = 0; i < a.length; i++ ) {
      found = false;
      for ( j = 0; j < b.length; j++ ) {
        if ( a[ i ] === b[ j ] ) {
          found = true;
          break;
        }
      }
      if ( !found ) {
        result.push( a[ i ] );
      }
    }
  
    return result;
  }
docs: Returns a new Array with the elements that are in a but not in b