How do I insert an element before everything else on a document?

Question

I don't think I can use insertBefore() because I do not know what element will be first in the DOM.

I am trying to insert a body tag (i.e. <body>).

Pat · Accepted Answer

Without using a library, try this:

document.body.insertBefore(document.createElement("div"), document.body.firstChild);

Matías Fidemraizer · Answer

Well, but you can always check this:

If document body has at least one child, use document.body.insertBefore([the new element], document.body.firstChild)
If document body has no children, just use document.body.appendChild([the new element]).

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