How to properly declare a php function as a variable in another function

Question

I'm looking to display a piece of javascript after the 6th paragraph of every post on my wordpress blog. So far, I can only get the function to work when I'm using a fixed variable:

add_filter( 'the_content', 'prefix_insert_post_ads' );
function prefix_insert_post_ads( $content ) { 
 $ad_code = 'fixed variable such as <div>box</div>';
 if (is_single()) {
 return prefix_insert_after_paragraph( $ad_code, 6, $content );
 }
 return $content;
}
function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
 $closing_p = '</p>';
 $paragraphs = explode( $closing_p, $content );
 foreach ($paragraphs as $index => $paragraph) {
 if ( trim( $paragraph ) ) {
 $paragraphs[$index] .= $closing_p;
 }
 if ( $paragraph_id == $index + 1 ) {
 $paragraphs[$index] .= $insertion;
 }
 }
 return implode( '', $paragraphs );
}

The javascript I'm trying to add:

function ad_unit() ?>
 <script type="text/javascript">
 ad = document.getElementById('marker');
 if (ad.getBoundingClientRect().width) {
 adWidth = ad.getBoundingClientRect().width; 
 } else {
 adWidth = ad.offsetWidth; // for old IE 
 }
 /* Choose the right ID */
 if ( adWidth >= 600 )
 aId = ["test1"]; 
 else if ( adWidth >= 468 )
 aId = ["test2"]; 
 else
 aId = ["test3"]; 
 document.write (
 '<div id="' + akId[0] + '"></div>'
 );
 </script>
<?php

I've tried to declare $placeholder = ad_unit(); but it keep displaying the unit at the top of the content instead of after the 6th paragraph. Somehow the prefix_insert_after paragraph function doesn't work after I add the javascript function. Any ideas?

Answer 1

Try it with ob_start() and ob_get_clean()

function ad_unit() 
{ 
 ob_start();
 ?>
 <script type="text/javascript">
 ad = document.getElementById('marker');
 if (ad.getBoundingClientRect().width) {
 adWidth = ad.getBoundingClientRect().width; 
 } else {
 adWidth = ad.offsetWidth; // for old IE 
 }
 /* Choose the right ID */
 if ( adWidth >= 600 )
 aId = ["test1"]; 
 else if ( adWidth >= 468 )
 aId = ["test2"]; 
 else
 aId = ["test3"]; 
 document.write ('<div id="' + akId[0] + '"></div>');
 </script>
 <?php
 return ob_get_clean();
}

So what happens is that with ob_start() you enable output buffering. You output the HTML but buffer it, then with ob_get_clean() you get the buffered output from the output buffer.

This will be cleaner without a function (and definitely work, I don't remember what plain HTML does when put in a PHP function):

// Somewhere above the rest of your application
ob_start(); ?>
/// YOUR HTML/javascript
<?php
$advertisement = ob_get_clean();

• Daniel W.: output buffers are really great, you can capture what would get sent to the browser w/o it, instead save the buffer into a variable
• Liwii: WOOT. Thanks man! That did the trick. I wasn't aware how useful ob_start(); and ob_get _clean(); are. I read a little bit on PHP.net but damn it's really confusing. By the way, is this a better way of calling hardcoded html/js then simply closing the php tags to include html/js?
• AmazingDreams: Sometimes stuff you put in functions are not supposed to be shown where you call the function. Using the output buffer guarantees this. Even if you are absolutely 100% sure that the function will only be called where the output is supposed to be, use the output buffer. Plans change. This might be an interesting read: web.archive.org/web/20101216035343/http://dev-tips.com/featured/…

Answer 2

You need opening and closing brackets for the php function

 <?php
 function ad_unit() { ?>
 <script type="text/javascript">
 ad = document.getElementById('marker');
 if (ad.getBoundingClientRect().width) {
 adWidth = ad.getBoundingClientRect().width; 
 } else {
 adWidth = ad.offsetWidth; // for old IE 
 }
 /* Choose the right ID */
 if ( adWidth >= 600 )
 aId = ["test1"]; 
 else if ( adWidth >= 468 )
 aId = ["test2"]; 
 else
 aId = ["test3"]; 
 document.write (
 '<div id="' + akId[0] + '"></div>'
 );
 </script>
 <?php }

• elitechief21: In the code you posted you were missing open and closing brackets, so unless the function ad_unit goes on beyond the line:<?php and you have a closing bracket for it after that line than you are missing the closing bracket as well