Running on Windows requires a bit of a hack. From the README:

gopherjs uses your platform's default GOOS value when generating code. Supported GOOS values are: linux, darwin. If you're on a different platform (e.g., Windows or FreeBSD), you'll need to set the GOOS environment variable to a supported value. For example, GOOS=linux gopherjs build [package].

So, try

GOOS=linux gopherjs build filename.go

What a non-sense. Can you just fix that?

I added GOOS=linux to my system environment variables and the restarted VSC and then ran gopherjs build filename.go and it worked!!
Thank you with all my heart.

Although now suddenly after making those changes I have now tried go run filename.go fails to compile go files with error exec: "C:\Users\me\AppData\Local\Temp\go-build012283026\b001\exe\filename": file does not exist

I have not seen this error until now and assume that it must be related to the changes that have occurred . I assume that some how these few changes have now confused Go and caused the problems has this happened to anyone else, and yet again I am stuck.

removing the added GOOS=linux variable from my system variables allows go run to work correctly again. Is there not a solution where i can have both Go and Gopherjs working at the same time or is it so extreme that i will have to wait for some one out there to make gopherjs compatible with windows or worse resort to changing my operating system !!

Don't set GOOS system wide, only set it for that session. I think the command is

set GOOS=linux
gopherjs build filename.go

but it might be setenv. I imagine you could easily write a script, even in Windows, to do this on a command-by-command basis.

This has been working this way (or broken this way, if you like) for a while. I think if the maintainers were going to fix it, they would have.

@EchoofthePast do not add GOOS=linux to your system. As the result you will get ELF binaries when you compile regular *.go programs instead of Windows binaries, so they won't run on Windows. This problem is bug and must be fixed.

using set GOOS=linux works its the correct command and works to build the files.
This may only be a small problem and once you have the solution to it can be easy to remember but I think this problem can also prove to discourage newer programmers from using Go and Gopherjs,
I thank you both for your help . I am truly grateful.

I hit the same issue in the past. I think it can be mitigated. I don't know if have any side-effect, I didn't test it in all cases, but for simply gopherjs build it works. Running the go test all tests works, with the exception of the fixedbugs/*, which all fails.

Just include this 4 lines at func init():

if build.Default.GOOS == "windows" {
	fmt.Fprintf(os.Stderr, "GOOS is Windows. The GopherJS is falling back to GOOS=linux\n")
	build.Default.GOOS = "linux"
}

Showing a message for the use is good, in my option, so this change is noticible and not silent.

Thank you to everyone.