How to enterVR without click vrButton

I want to go into VR mode once I open the project, and I have tried vrhelper.enterVR() and engine.enterFullscreen(). But sometime I cannot render the full screen all the time via these two commands, and it shows me the following warning and errors:
console warn:Failed to execute ‘requestFullscreen’ on ‘Element’: API can only be initiated by a user gesture.
console error:Uncaught (in promise) TypeError: fullscreen error

I have also tried the following method, but it doesn’t fix the problem:
What I want is to jump from one VR project to another and keep VR mode instead of manually clicking VR button to re-enter.

/*This is not possible because it’s not allowed to execute this action without user input (as the console says).

You could use a info or start screen and when the user closes this screen, you can enter VR in the same moment. But the user has to click something.*/

I haven’t read your last sentence sorry. It is possible if you were already in VR before.
You have to grab the vrdisplayactivate event from your browser:

This ‘counts as’ a user click and you can enter VR when this event gets fired.

I use this code but it’s not always effective
when i use htc vive and already in VR before,jump from my project to another,firefox browser will show loading screen for long time,i have to quit from VR to break this loading