Javascript: Photo Gallery with Forward/Back Button

Question

I'm super new to Javascript and trying to make a front and back button to move through a set of images.Below is what I'm doing but it just wont' work. I added an alert to the beginning of both functions and they worked so I know the functions are being called. Please help!

HTML:

Javascript:

 var which=0;
 var photos=new Array();
  photos[0]='images/gallery/airport.jpg';
  photos[1]='images/gallery/vancouvercenter.jpg';
  photos[2]='images/gallery/translatorjudges.jpg';
  photos[3]='images/gallery/emmaplaying.jpg';
  photos[4]='images/gallery/kate.jpg';
  photos[5]='images/gallery/plushies.jpg';
  photos[6]='images/gallery/juniors.jpg';
  photos[7]='images/gallery/pikachucamera.jpg';
  photos[8]='images/gallery/dressup.jpg';
  photos[9]='images/gallery/sandiego.jpg';
  photos[10]='images/gallery/signedbox.jpg';
  photos[11]='images/gallery/top42013.jpg';
  photos[12]='images/gallery/5.JPG';
  photos[13]='images/gallery/airportplay.jpg';
  photos[14]='images/gallery/piplup.jpg';
  photos[15]='images/gallery/2.JPG';
  photos[16]='images/gallery/booze.jpg';
  photos[17]='images/gallery/dice.jpg';
  photos[18]='images/gallery/akinator.jpg';
  photos[19]='images/gallery/sleeping.jpg';

 function backward(){
     if (which>0){
      which=which-1;
      }
     document.GetElementbyId("gallery").src=photos[which];
     }

  function forward(){
     if (which<photos.length-1)
     {
     which=which+1;
     }
    document.GetElementbyId("gallery").src=photos[which];
    }

Answer 1

Might be as simple as changing GetElementById to getElementById