IT350 - Web and Internet Programming

Lab 06 ? Game Time!


You?ve come a long way with JavaScript, and last week we learned about how to truly make our pages come alive by changing the content dynamically. For our JavaScript finale, you?ll practice your knowledge by creating a web page to play the ?8-puzzle.?

The 8-puzzle consists of a 3x3 grid with 8 tiles. The one missing tile enables other tiles to move around. After shuffling the puzzle, the goal is to reconstruct the original picture or configuration. This game has been very often used for research into artificial intelligence, and its properties are well studied.


You must create a folder on you Web drive called "Lab06" (without the quotes) and store your work in that directory. This lab does NOT draw on the previous labs, so there is no need to copy your old web pages into this directory.

This week you will make a single web page, game.html, that plays the 8-puzzle. We are giving you some starter code, which you must improve upon. Here is how the game should operate:

  1. This is a list of requirements ? be sure to read the ?Suggested Approach? below!
  2. When the page is first loaded, it should look like the following. The starter code already does this for you:
  3. (4 points) When the user clicks ?Load Puzzle?, it should replace the monkeys with appropriate images to fill in the picture as shown below. You must copy the appropriate image filenames from the ?TileArray? that is given in the starter code. Once the game starts, your ?Load Puzzle? button is not required to do anything, though resetting the game would be a nice touch.
  4. (5 points) When the user clicks on a tile, you should shift that tile into the ?hole? in the puzzle, if the hole is directly adjacent to that tile (not diagonally). If the tile is not adjacent, you should popup an error message. You must keep track of the new tile layout in the given ?TileArray? ? don?t just change the images.
    For instance, here is the result after clicking on the middle tile in the last row.
  5. (5 points) When the user clicks on the ?Shuffle? button, you should do three things:
    a.) Check that the ?Number of steps to shuffle? is between 1 and 20. If not, warn the user and do nothing.
    b.) Otherwise, set the background color for the whole table to the value given in the ?Background color? input box.
    c.) Shuffle the tiles, based on the number given in the ?Number of steps to shuffle? input box. So if that number is 5, you would do the following 5 times: randomly pick a tile that is able to move, and move it into the ?hole? spot. You must make only legal moves ? always moving some tile that is adjacent to the hole, but randomly choosing among those so eligible. (If you just randomly shuffle pieces around, there is a 50% chance that you end up with a puzzle that can?t be solved). However, you are not required to slowly animate the results of the shuffle like the demo version of the puzzle does (see extra credit). Instead, you can just show the results after making all the moves.
    It?s not required, but a nice touch is insisting that the random move doesn?t move the hole back to where it just came from. So 2 random moves never leaves the hole where it started.
    So after shuffling 2 more tiles and setting the background color to red your page might look like this:
  6. You must use JavaScript and Dynamic HTML to accomplish this.
  7. (2 points) You must make appropriate use of functions to break up your code.
  8. (1 point) As always, you should have appropriate comments. As a start, each function should have a brief summary of its purpose.
  9. (1 point) Your default.htm page should have a link to your new game.html

Your web page must be constructed using Notepad or a similar text-only editor. The use of programs such as Microsoft Word, Microsoft Frontpage, DreamWeaver, ColdFusion, Mozilla Composer, etc. will be considered an honor offense.

Suggested Approach

You can create your puzzle to meet the above requirements in any way you like, provided of course you write your own code and follow all course policies.


However, you may find this lab more challenging. Unless you feel very confident, we suggest that you approach this lab by following this sequence of steps:


  1. Follow this step precisely: Download the starter code by right-clicking on the link, pick ?Save As?, then choose ?Web Page HTML only?. Save it as game.html in your new Lab06 directory. Using ?View Source? and saving the results is not recommended.
  2. Before you proceed, make sure you understand how everything works in the starter code. Look carefully at the given testFunction() to see how to use 2-dimensional arrays.
  3. Write a function loadImagesFromArray() to copy the image filenames from TileArray to the images in the table (replacing the monkey images). As a test, add a call to loadImagesFromArray() at the very end of the file (where testFunction() was called). When this works, leave the test call to loadImagesFromArray() in place for now.
    (You should not copy the image files to your own directory ? just leave them on the server).
  4. Write a function moveImage(row, col) that moves the tile in location (row, col) to the current location of the hole (this implies you?ll need to keep track of where the hole is). Perform the move first in the TileArray, then call loadImagesFromArray() to copy the result to the images. Test this by adding a call to moveImage(1,1) to the end of your HTML file.
  5. Once that works, delete the test calls to loadImagesFromArray() and moveImage(1,1) from the end of your HTML file.
  6. Add the appropriate HTML to call loadImagesFromArray() when the user clicks on ?Load Puzzle.?
  7. Add the appropriate HTML to call moveImage() appropriately when the user clicks on one of the images.
  8. Modify moveImage() so that it checks appropriately for an illegal move (if the user clicks on a tile that can?t move). Think carefully on paper how to compute this mathematically ? if you do it right this should be a small function.
  9. Write appropriate code to make a bunch of random, legal moves when the user clicks on ?Shuffle.?
  10. Write appropriate code so that the script also sets the table background appropriately when the user clicks on ?Shuffle.?
  11. Check that you have good documentation and make appropriate use of functions.
  12. Check that you have met all the Requirements given above.


Extra Credit

For a nominal amount of extra credit do some/all of the following:

1.      Ex #3 on slides set #10 ? Arrays and Objects:: What is the output of the following JavaScript snippet (write the answer on the Lab coversheet or extra sheet of paper and turn it in with your lab)?


function changeMe1( z ) {

z[0] = 75;


function changeMe2( a, b) {

a = b;


var array1 = [17, 21, 42];

var array2 = [14, 19];

var array3 = [7, 8, 9];

var x = 63;

changeMe1 (array1);

document.writeln("<br/> array1: ", array1);

changeMe1 (x);

document.writeln("<br/> x: ", x);

array1 = array2;

document.writeln("<br/> array1: ", array1);

changeMe2 (array1, array3);

document.writeln("<br/> array1: ", array1);


Extra credit related to this lab (NOTE: saving a backup copy of your working lab is recommended before starting on this):

2.      Make your shuffle operation move slowly, showing the results briefly after each move, like the demo version that was shown in the lab.

3.      Make your shuffle operation move very smoothly from one location to another (not jumping from (1,1) directly to (1.2).
HINT: you?ll need to ditch the table and just use absolute CSS positioning to make this work.

4.      Make your program work with more than one ?hole? (e.g. two missing tiles). Create some natural user interface for this to deal with the ambiguity that arises when the user clicks on a tile that could move into either of the holes.

5.      Super bonus points: make your program work on any image, given just a single JPG file for that image. Suggestion: use multiple copies of your image on the page, CSS relative positioning, and layers.


  1. Your main web page should be called "game.html" (without the quotes).
  2. You must meet all the Requirements given above.
  3. All of your files should be in a folder called "Lab06" (without the quotes) on the W drive. Your instructor will assume that your web pages are viewable at where XXXXXX is your alpha number. You may want to check that this URL is viewable and that everything works correctly from a computer where somebody else is logged in. If you've goofed and linked to a file on your X drive, this will help you catch it!
  4. Turn in the following hardcopy at the beginning of class on the due date, stapled together in the following order (coversheet on top):
    1. A completed assignment coversheet. Your comments will help us improve the course.
    2. A printout of the source to your Lab06/game.html file.
    3. If you use any external script files, include a printout of those too.


         You do not need to (and should not) reload the page to make any of this work ? use DHTML to make changes happen on the fly.

         You can set the ?src? attribute of an image to change what image it is displaying. However, trying to read this attribute is not recommended because the results you get back will vary.

         If your code doesn't work, look to see if your script tag has an extra space before "text/javascript" like this:
<script type =" text/javascript" src = "script.js">
If so, change it to like this:
<script type ="text/javascript" src = "script.js">
This matters whether or not you use an external JavaScript file. This space is inserted by Firefox when you do ?View Source.?

         If you want to use an external script file, we suggest the following syntax. Otherwise, the browser may ignore later <script> tag if you try to include JavaScript inline in your document. Use this:
<script type = "text/javascript" src="calc.js" > </script>
Instead of using:
<script type = "text/javascript" src="calc.js" />