# go-promises

Return promises from Go WASM.

## Usage

Write some go code, like this.

```go
import (
    "syscall/js"

    promises "codeberg.org/danjones000/go-promises"
)

func Add(a, b int) int {
    return a + b
}

func AddWrapper() value.JSWrapper {
    return func(this js.Value, args []js.Value) (any, error) {
		if len(args) < 2 {
			return nil, errors.New("add called with too few arguments")
		}
		a := args[0]
		b := args[1]

		if a.Type() != js.TypeNumber {
			return nil, fmt.Errorf("First argument must be a number. %s given", a.Type())
		}

		if b.Type() != js.TypeNumber {
			return nil, fmt.Errorf("secong argument must be a number. %s given", b.Type())
		}

        return Add(a.Int(), b.Int()), nil
    }
}

func main() {
    js.Global().Set("add", promises.PromisifyGoFunc(AddWrapper()))
	<-make(chan struct{})
}
```

Next, compile this code:

```shell
GOOS=js GOARCH=wasm go build -o ./app.wasm ./
```

Copy the `app.wasm` file, as well as the `wasm_exec.js` from your go installation, into wherever you have your web files located.

```shell
cp app.wasm "$(go env GOROOT)"/misc/wasm/wasm_exec.js path/to/web/
```

Finally, you'll need some frontend code like this:

```javascript
const go = new Go();
WebAssembly.instantiateStreaming(fetch("app.wasm"), go.importObject).then((result) => {
    go.run(result.instance);
});
```

Now, the "add" function is available anywhere in your javascript.

## Roadmap

- [ ] Argument validation, so you can write less code in your wrapper function.
- [ ] An easy method for attaching functions to other objects, so they don't have to be in the global scope