Why does run fail after I compile a GoLang project to Web Assembly?

Question

I created a Go(lang) project in Visual Studio Code. I created a main.go file that I will compile to WebAssembly, and another main.go that I will run as a server (to serve my Web Assembly glue file).

For reference, I'm following the tutorial here: https://golangbot.com/webassembly-using-go/

In a Visual Studio Code terminal, I do the following:

[cd to my wasm source folder with the first main.go]

${env:GOOS} = "js" ${env:GOARCH} = "wasm"

go build -o ../../assets/json.wasm

[cd to my server folder with the other main.go]

go run main.go

[I get the following error]

exec: "C:\Users\...\AppData\Local\Temp\go-build3258126417\b001\exe\main": file does not exist

I was able to run this server prior to the build. What's going on?

This should have just run. But now I'm not able to run the server. I get that strange "file does not exist" error.

Answer 1

I spent a lot of time trying to figure this out and finally got it! Here's the deal:

Either or both of the GOOS and GOARCH environment variables that are required by the build go command (for webassembly) seem to conflict with the go run command. I don't know why. I discovered this in a backwards kind of way.

(TLDR: use different terminals to build and run and don't set these environment variables globally -- set them prior to every build. Use the Terminal>Split Terminal to maintain the build settings between tests! ).

Using the Visual Studio Code Powershell terminal, I set these 2 variables (or so I thought) and then ran the build. Then I ran the server to try to see the fruits of my labor and got a strange error in the Chrome console (something about expecting one magic word but receiving another). It turns out this error is fairly generic and after some googling, determined it probably meant something happened with my build. After trying a few more times unsuccessfully to build, I decided to set the environment variables in windows (as SYSTEM variables) so that I didn't have to keep setting them when I did my build.

I built again (still no build errors), but then when I went to run the server, I got the

exec: "C:\Users...\AppData\Local\Temp\go-build3258126417\b001\exe\main": file does not exist

error. At this point, I couldn't run any of my Go servers in any project. Since the only "global" thing I'd done was set those 2 environment variables, I decided to remove them. I could now run my Go servers. But I still couldn't execute my builds in the browser. What's going on??

I figured that since setting the global environment variables had an effect (albeit, a negative effect) whereas I hadn't experienced that issue when manually setting them directly in the terminal prior to each build, then maybe there was something wrong with the way I was setting the variables (I don't use Powershell very often).

After more googling and some experimentation, I discovered the "correct" way to set these variables in the terminal (noted in my original question). So manually setting them (the right way) prior to the build fixed the build issue (it wasn't building correctly since those variables weren't being set properly).

Now I knew the variable were getting set properly because now I was getting that error when I set them manually prior to the build. So now what?

I killed the terminal after build, and then started a new terminal, and the run was successful.

So bottom line: the GOOS and GOARCH environment variables should not be set when running a server, so don't start a server in the same terminal that you used to build the web assembly code!