goes

A proof-of-concept that shows that Go(lang) WASM can be turned into regular javascript that runs in IE11.

Check out the demo over here here. If you open the developer console in ie11, youll see the Go code do its work. In any other browser you can add an "#emscripten" hash and reload the page to force the use of the javascript version (instead of using wasm).

How it works

We compile the Go code to wasm: GOOS=js GOARCH=wasm go build -o main.wasm
We use the binaryen wasm2js tool to turn it into emscripten js: wasm2js --emscripten -O main.wasm -o hello_go.js
We add the following js: var go = new Go(); to the beginning of the output file

And at the end of that same file, add the following js:

    var asm = instantiate({
          runtime_resetMemoryDataView: go.importObject.go["runtime.resetMemoryDataView"],
          runtime_wasmExit: go.importObject.go["runtime.wasmExit"],
          runtime_wasmWrite: go.importObject.go["runtime.wasmWrite"],
          runtime_nanotime1: go.importObject.go["runtime.nanotime1"],
          runtime_walltime1: go.importObject.go["runtime.walltime1"],
          runtime_scheduleTimeoutEvent: go.importObject.go["runtime.scheduleTimeoutEvent"],
          runtime_clearTimeoutEvent: go.importObject.go["runtime.clearTimeoutEvent"],
          runtime_getRandomData: go.importObject.go["runtime.getRandomData"],
          syscall_js_finalizeRef: go.importObject.go["syscall/js.finalizeRef"],
          syscall_js_stringVal: go.importObject.go["syscall/js.stringVal"],
          syscall_js_valueGet: go.importObject.go["syscall/js.valueGet"],
          syscall_js_valueSet: go.importObject.go["syscall/js.valueSet"],
          syscall_js_valueIndex: go.importObject.go["syscall/js.valueIndex"],
          syscall_js_valueSetIndex: go.importObject.go["syscall/js.valueSetIndex"],
          syscall_js_valueCall: go.importObject.go["syscall/js.valueCall"],
          syscall_js_valueNew: go.importObject.go["syscall/js.valueNew"],
          syscall_js_valueLength: go.importObject.go["syscall/js.valueLength"],
          syscall_js_valuePrepareString: go.importObject.go["syscall/js.valuePrepareString"],
          syscall_js_valueLoadString: go.importObject.go["syscall/js.valueLoadString"],
          syscall_js_copyBytesToJS: go.importObject.go["syscall/js.copyBytesToJS"]
    }, {
          buffer: new ArrayBuffer(209715200)
    });

    go.run({
          exports:{
                run: asm.run,
                mem: asm.mem,
                resume: asm.resume,
                getsp: asm.getsp
          }
    });

we use babel to turn the wasm_exec.js into a es5 compatible version: npx babel wasm_exec.js --out-file wasm_exec_es5.js

we conditionally load all required polyfills for ie11, and finally run the program:

```html
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">

<script type="text/javascript">
      
      // should target ie11 or below: https://stackoverflow.com/questions/29987969/how-to-load-a-script-only-in-ie
      if(/MSIE \d|Trident.*rv:/.test(navigator.userAgent) || window.location.hash === "#emscripten") {
            if(window.msCrypto) {window.crypto = window.msCrypto;}
            document.write('<script src="https://cdn.jsdelivr.net/npm/text-encoding@0.7.0/lib/encoding-indexes.js"><\/script>');
            document.write('<script src="https://cdn.jsdelivr.net/npm/text-encoding@0.7.0/lib/encoding.min.js"><\/script>');
            document.write('<script src="https://unpkg.com/core-js-bundle@3.6.5/minified.js"><\/script>');
            document.write('<script src="https://cdn.jsdelivr.net/npm/regenerator-runtime@0.13.7/runtime.min.js"><\/script>');
            document.write('<script src="wasm_exec_es5.min.js"><\/script>');
            document.write('<script src="hello_go_after.min.js"><\/script>');
      } else {
            window.wasmExecLoaded = function() {
                  const go = new Go();          
                  if (WebAssembly.instantiateStreaming) {
                        
                        // chrome 
                        WebAssembly.instantiateStreaming(fetch("main.wasm"), go.importObject).then(function(result) {
                              go.run(result.instance);
                        });          
                  
                  } else {
                        
                        // safari
                        fetch('main.wasm').then(function(response) {
                              return response.arrayBuffer()
                        }).then(function(bytes) {
                              return WebAssembly.instantiate(bytes, go.importObject)
                        }).then(function(result) {
                              return go.run(result.instance)
                        });
                  }
            }
            
            document.write('<script onload="window.wasmExecLoaded()" src="wasm_exec.js" defer><\/script>');
      }
</script>

<title>Goes Demo</title>
</head>
<body>

</body>
</html>
```

Known Issues

This might break with further go version as the wasm_exec.js sometimes changes
The emscripten js files become very large: 17MB unminified and ungzipped
The text encoding/decoding doesn't seem to be 100%, unexpected symbols and whitespaces while printing exotic characters
On IE11 window.msCrypto is used, this may have security implications.
Expect a considerable slow down, i've only tested ie11 in a vm but it took 3-4 minutes to run a [Fib(40)](https://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go) call while normally about 2s to run the same as regular wasm in a browser
The required memory allocated for the wasm byte array is currently hardcoded and very large (200MiB)

advdv/goes

goes

How it works

Known Issues

TODO