Return V8Object is endless iterable

The following script produces an endless steam of lines containing "test: test":

    <?php
    
    $jscript = new V8Js();
    $jscript->executeString("values = {}");
    $jscript->executeString("values['test'] = 'test'");
    $values = $jscript->executeString("values");
    
    foreach ($values as $key => $value) {
        echo "$key: $value\n";
    }