Getting the content of a meta tag

Hi there,
i want to get the content of this meta tag

<meta property="article:content_tier" content="locked">

I tried it with the ececuteJavascript addon:
document.querySelector("meta[property="article:content_tier"]").getAttribute('content')

After the execution of this code, i want to validate it by comparing it to the word locked, but it does not compare. Is my code wrong?