Auto Fullscreen

So basically just started using unity (it's fun but difficult, i like it tho) and i want my game, (tutorial roll a ball game) which is hosted on my website to auto fullscreen. Not really good with HTML, but i did figure out that this:

Code (HTML):

1. gameInstance.SetFullscreen(1)

when the fullscreen button is clicked, runs. I have tried various ways of getting this snippet of code to run on page load, but ELI5 what i need to adjust in my index.html to make this auto fullscreen on page load.

Edit: the game is in WebGL

 

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