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The power of repetition - PHP

Did you ever have one of those sites that started out small, but kept growing and growing? Adding new pages to a site or removing old ones can often take more time than developing the pages themselves.

  1. Dynamic Generation of Menu Structures and JavaScript Rollovers in PHP
  2. Making a Template
  3. Starting to Automate
  4. The power of repetition
  5. Ordering up a Menu
  6. Adding Pages
By: Chris Mospaw
Rating: starstarstarstarstar / 11
May 10, 1999

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Computers sure do tolerate repetitive counting tasks a lot better than I do, and PHP takes maximum advantage of that by allowing stepping through each part of the $SITE_PAGES array, generating the necessary pointers for the JavaScript, as well as the appropriate buttons and links to other pages.

Once the basic page layout and JavaScript are set up, setting up the automation is pretty much a matter of echoing either a numeric value (in the case of JavaScript pointers) or part of an array (in the case of links to other pages in the menu).

Replacing a few lines of the JavaScript shown earlier with some PHP yields this code:

<script language="JavaScript"> <!-- This script controls the rollovers in the menu area if (document.images) { <? // Changed code begins here! $counter = sizeof($site_pages); $i = 0; do { $item = $i + 1; echo " image" . $item . "off = new Image();\n"; echo " image" . $item . "off.src = \"$site_pages[$i]-off.gif\";\n"; echo " image" . $item . "on = new Image();\n"; echo " image" . $item . "on.src = \"$site_pages[$i]-on.gif\";\n"; echo " otherImage" . $item . " = new Image();\n"; echo " otherImage" . $item . ".src = \"$site_pages[$i]-b.gif\";\n"; echo "\n"; $i++; } while ($i < $counter); // Changed code ends here! ?> otherImageDefault = new Image(); otherImageDefault.src = "default.gif"; } function changeImages() { if (document.images) { for (var i=0; i<changeImages.arguments.length; i+=2) { document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src"); } } } // --> </script>

Line 7 gets the number of items in the array $SITE_PAGES (which is defined in PAGES.HTML) and assigns it to a counter used in the DO loop defined in lines 10 through 23. Line 11 assigns the $ITEM variable in order to allow us to start the JavaScript definitions at 1 instead of 0. Line 21 increments the place holder variable $I.

During the development of this project, some limitations of the PHP parser were encountered, but fixed with the "." (string concatenation) command used in the echo lines. Without this workaround, the code would have read:

echo "image$itemoff = new Image();\n";

which PHP (understandably) chokes on. Whenever you use variables that are embedded in the middle of other text, it's best to use the "." command to tie things together rather than relying on the PHP parser to figure out what you want.

The rest of the JavaScript remains the same because the other items only need to be defined once, and there's no practical reason to embed it within PHP.

>>> More PHP Articles          >>> More By Chris Mospaw

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