ChildNodes of DOMDocument lost order - php

Question

I have a html string. I want to traverse it and extract some information. My code is as following:
$str = '<p>aaa</p><img src="http://stackoverflow.com/questions/ask"/><p>sss</p><img src="http://stackoverflow.com/"/>';
function parseContent($str) {
$contents = array();
$dom = new DOMDocument('1.0', 'UTF-8');
if (!$dom->loadHTML($str)) {
return $contents;
}
$stack = array($dom);
while (count($stack) > 0) {
$node = array_shift($stack);
foreach ($node->childNodes as $node) {
if ($node->hasChildNodes()) {
$stack[] = $node;
} else {
switch ($node->nodeType) {
case XML_ELEMENT_NODE:
if ('img' == $node->tagName) {
$contents[] = $node->attributes->getNamedItem('src')->nodeValue;
}
break;
case XML_TEXT_NODE:
$contents[] = $node->textContent;
break;
}
}
}
}
return $contents;
}
The problem is: When I dumped the return value of this function, it was something like this:
array(
'http://stackoverflow.com/questions/ask',
'http://stackoverflow.com/',
'aaa',
'sss',
)
Could someone point it out why the order was lost?

Answer 1

Extending from comment:
That's because each <p> also has child node (a text node), so they go into the first if ($node->hasChildNodes()) statement and are stacked one more time.
To avoid this, one way is to add one more condition:
/* ... */
if ($node->hasChildNodes()) {
if ($node->childNodes->length==1 && $node->childNodes->item(0)->nodeType==XML_TEXT_NODE) {
$contents[] = $node->childNodes->item(0)->textContent;
} else {
$stack[] = $node;
}
} else {
/* ... */