How to write functions to create and AppendChild HTML elements in PHP?

Question

I want to write functions that create HTML elements and append child elements to each other, rather than echoing large chunks of HTML code or using echo <<<HEREDOC.

The

createLoginBar function will create a div that I will append to other HTML elements into my createLogoutBanner function.

function createLoginBar() {
    $dom = new DOMDocument();
    $login_bar = $dom->createElement('div');
    $login_bar->setAttribute("id", "login_bar");
    $dom->appendChild($login_bar);
    return $dom->saveHTML();
}

function createLogoutBanner() {
    $dom = new DOMDocument();
    $login_bar = createLoginBar();
    $login_flex = createBlankLoginFlex();
    $banner_login_form = createBannerLoginForm();
    $login_message_flex = createLoginMessageFlex();
    $nonmember_signup_flex = createNonSignupFlex();
    $not_a_member_form = createNotAMemberForm();

    $dom->appendChild($login_bar); //This line gives an error
    $login_bar->appendChild($login_flex);
    $login_flex->appendChild($banner_login_form);
    $login_bar->appendChild($login_message_flex);
    $login_bar->appendChild($nonmember_signup_flex);
    $nonmember_signup_flex->appendChild($not_a_member_form);
    return $dom->saveHTML();
}

createLogoutBanner The line $dom->appendChild($login_bar); in the function gives an error:

Fatal Error: Uncaught TypeError: DOMNode::appendChild(): Parameter #1 ($node) must be of type DOMNode, given in string.

Answer 1

Due to error condition DOMNode::appendChild() expected to be passed a DOMNode.
Your createLoginBar function returns a string instead of a node.
Try the following changes:

function createLoginBar() {
    $dom = new DOMDocument();
    $login_bar = $dom->createElement('div');
    $login_bar->setAttribute("id", "login_bar");
    $dom->appendChild($login_bar);
    return $dom; //->saveHTML();
}

Then you will see the error Fatal Error: Uncaught DOMException: Bad Documentation Error. This is because you must use the same parent instance of the DOMDocument to create the child nodes. Instead of creating a new DOMDocument in each function, create a top-level DOMDocument and pass it to each function to use.

function createLoginBar(DOMDocument $dom):DOMNode 
{
    $login_bar = $dom->createElement('div');
    // the following line will cause invalid html if this function is called more than once
    $login_bar->setAttribute("id", "login_bar");

    return $login_bar;
}
function createBtn(DOMDocument $dom, string $value):DOMNode 
{
    $btn = $dom->createElement('button', $value);
    $btn->setAttribute("class", "widget");

    return $btn;
}

$dom = new DOMDocument();
$login_bar = createLoginBar($dom);
$login_btn = createBtn($dom, 'login');

$login_bar->appendChild($login_btn);

$dom->appendChild($login_bar);

echo $dom->saveHTML();

result:

login

sandbox