getElementsByTagName()

getElementById and getElementsByTagName are methods of the PHP DOMDocument class. These methods can be used in PHP to get elements from a HTML document.
- Before to use the methods of the PHP DOMDocument class, you must load the HTML document into a DOMDocument object, like in this code:

// create the DOMDocument object
$dochtml = new DOMDocument();

// load content from a HTML page (or file)
$dochtml->loadHTMLFile('filename.html');

// OR, load the HTML items from a string containing the HTML document
$strhtml = '<html><body>Tags and content.<br></body></html>';
$dochtml->loadHTML($strhtml);
- The $dochtml contains an object with a tree structure of all elements in a HTML document. After this object is created, you can use the DOMDocument methods to access the HTML items (as you can see in the examples below).
- It is indicated to have HTML well-formed, otherways may generate E_WARNING errors when it encounters bad markup.

To traverse the elements of a PHP object, use the foreach() loop instruction.

getElementById

The getElementById('ID') function returns an object that contains the element with a given ID, or NULL if the element is not found.
This function is useful when you want to read the content, or attribute value of a HTML element with a specified ID.
    - Use the nodeValue property to get the content of the element returned by getElementById().
    - Use the tagName (or nodeName) property to get the name of the tag.

Example, gets the tag name and content of the element with a specified ID:
<?php
$strhtml = '<!doctype html>
<html>
<head>
 <meta charset="utf-8" />
 <title>PHP getElementById, getElementsByTagName</title>
</head>
<body>
 <div id="dv1">http://coursesweb.net</div>
</body></html>';

// create the DOMDocument object, and load HTML from a string
$dochtml = new DOMDocument();
$dochtml->loadHTML($strhtml);

// get the element with id="dv1"
$elm = $dochtml->getElementById('dv1');

// get the tag name, and content
$tag = $elm->tagName;
$cnt = $elm->nodeValue;

echo $tag. ' - '. $cnt;           // div - http://coursesweb.net
?>

getElementsByTagName

The getElementsByTagName('tag') function returns an object that contains all the elements with a given local tag name. The special argument '*' matches all tags.
This function is useful when you want to read the content, or attribute of multiple HTML elements that have the same <tag>.
    - Use the getAttribute('attribute') to get the value of a specified attribute.

Example, gets, and outputs the ID and content of each DIV:
<?php
$strhtml = '<!doctype html>
<html>
<head>
 <meta charset="utf-8" />
 <title>PHP getElementById, getElementsByTagName</title>
</head>
<body>
 <div id="cweb">http://coursesweb.net</div>
 <p>Free PHP Course</p>
 <div id="mp">www.MarPlo.net</div>
</body></html>';

// create the DOMDocument object, and load HTML from a string
$dochtml = new DOMDocument();
$dochtml->loadHTML($strhtml);

// gets all DIVs
$divs = $dochtml->getElementsByTagName('div');

// traverse the object with all DIVs
foreach($divs as $div) {
  // gets, and outputs the ID and content of each DIV
  $id = $div->getAttribute('id');
  $cnt = $div->nodeValue;

  echo $id. ' - '. $cnt. '<br/>';
}
?>

- You also can use /load only a part of the HTML document.
Example 2. Loads a string containing only the BODY part, store into an Array the content of each paragraph with class="cls".
<?php
$strhtml = '<body>
 <p class="cls">Free PHP Course</p>
 <p class="cls">URL: http://coursesweb.net</p>
 <p>Paragraph without class.</p>
 <div>www.MarPlo.net</div>
 <p class="cls">PHP getElementById and getElementsByTagName</p>
</body>';

// create the DOMDocument object, and load HTML from a string
$dochtml = new DOMDocument();
$dochtml->loadHTML($strhtml);

// gets all <p> tags
$prgs = $dochtml->getElementsByTagName('p');
$pcls = array();

// traverse the object with all paragraphs
foreach($prgs as $prg) {
  // if the current paragraph has class="cls", adds it in the $pcls array
  if($prg->getAttribute('class') == 'cls') {
    $pcls[] = $prg->nodeValue;
  }
}

// outputs the $pcls array
print_r($pcls);

// Array ([0] => Free PHP Course [1] => URL: http://coursesweb.net [2] => PHP getElementById and getElementsByTagName )
?>

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag renders as emphasized text, displaying the text oblique?
<strong> <pre> <em>
<p>Web development courses: <em>CoursesWeb.net</em></p>
Which CSS property defines the space between the element border and its content?
margin padding position
h3 {
  padding: 2px 0.2em;
}
Click on the method which returns the first element that matches a specified group of selectors.
getElementsByName() querySelector() querySelectorAll()
// gets first Div with class="cls", and shows its content
var elm = document.querySelector("div.cls");
alert(elm.innerHTML);
Indicate the PHP variable that contains data from a form sent with method="post".
$_SESSION $_GET $_POST
if(isset($_POST["field"])) {
  echo $_POST["field"];
}
PHP getElementById and getElementsByTagName

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