Why is this PHP DOM parse with getAttribute not working?

问题

From this page, I want to get the value of the input tag with the name form_key. But I get the following error:

Fatal error: Uncaught Error: Call to undefined method simple_html_dom::getAttribute() in test.php:9 Stack trace: #0 {main} thrown in test.php on line 9

Please note that I am using PHP Simple DOM parser.

PHP:

include('simple_html_dom.php');

$html = file_get_html('https://b2b.chiemsee.com/customer/account/login/');

if($html->getAttribute('name') =='form_key'){
    echo $html->nodeValue;
}

来源：https://stackoverflow.com/questions/56559115/why-is-this-php-dom-parse-with-getattribute-not-working