Go 1.18 drops syscall.js.Wrapper

[janpfeifer]

Because of performance reasons Go is dropping js.Wrapper. I noticed this today, as I was trying out the 1.18.1 beta.

I suspect it should be an easy fix, but I haven't yet dived into it. Hopefully the fix will be backwards compatible -- since it only removed functionality.

I'll try to do post benchmarking in a wasm game I occasionally develop.

[janpfeifer]

The fix is simple, but unfortunately I couldn't find a way not to break the API one way or another :\ So the *fromJS() methods will take js.Value. So from the examples, one cannot use something like a dom.Element as input to *FromJS() methods. Instead I'm adding the *FromWrapper() methods that will allow for that.`.

Fix seems to be working on all tests, both in go1.17 and go1.8.beta1 -- so the webapi will work on both versions of Go.

I'm also adding go.mod.

(I'll post the PR soon)

[janpfeifer]

The change is in, and seems to be working here (tests passing, and working in my WebGL application).

I also benchmarked on my WASM+WebGL game the time it took to draw a typical scene (maybe a thousand moving sprites), and it takes 10ms (only the drawing), and the difference from go 1.17 and go 1.18 was in the noise (lots of variance in the metric). Informally it felt go 1.18 was 0.5ms faster ... but certainly in the noise of my measure.