function funnyResize( arr, newElement, n )
{
  n >>= 0; // убеждаемся что целове
  if( n <= arr.length ) {
    arr.length = n;
    return arr;
  }
  n -= arr.length;
  var elements = [ newElement ];
  while( n > 1 ) {
    if( n & 1 )
      arr = arr.concat( elements );
    elements = elements.concat( elements );
    n >>= 1;
  }
  arr = arr.concat( elements );
  return arr;
}

alert( funnyResize( ["A","A","A"], "B", 10 ) );

Array.prototype.dobav = function( newElement, n ) {
  while( n-- )
    this.push( newElement  );
  return this;
}

alert( ["A","A","A"].dobav( "B", 4 ) );