MainEntityOfPage

I have an Article inside a Page and the json-ld for this page is:

{
    "@type": "Article",
    "mainEntityOfpage": "www.urlofthepage.com",
    ...
}

Basically in this page there is just one element.

Or should i declare also the Page? like this?
[
    {
        "@type": "WebPage"
        "@id": "idPage"
        ...
    }
    {
        "@type: "Article"
        "mainEntityOfPage": "idPage"
        ...
    }
]

Greetings