go-whosonfirst-export-wasm

Go package for compiling the Export method of the go-whosonfirst-export package to a JavaScript-compatible WebAssembly (wasm) binary. It also provides a net/http middleware packages for appending the necessary static assets and HTML resources to use the wasm binary in web applications.

Documentation

Build

To build the export_feature WebAssembly binary for use in your applications run the following command:

GOOS=js GOARCH=wasm go build -mod vendor -o export_feature.wasm cmd/export-feature/main.go

Use

To use the export_feature WebAssembly binary in your applications a JSON-encoded GeoJSON string to the export_feature function.

The function returns a JavaScript Promise that will return a JSON-encoded Who's On First (WOF) GeoJSON string on success or an error message if there was a problem.

	var str_f = '{"type": "Feature" ... }'	// A valid GeoJSON Feature
	
	export_feature(str_f).then(rsp => {
	    console.log("WOF-exported feature is ", rsp);
	}).catch(err => {
	    console.log("Failed to export feature: ", err);
	});

In order to load the export_feature function you will need to include the wasm_exec.js and whosonfirst.export.feature.js JavaScript files, or functional equivalents. Both scripts are bundled with this package in the static/javascript folder.

Middleware

The go-whosonfirst-export-wasm/http package provides methods for appending static assets and HTML resources to existing web applications to facilitate the use of the export_feature WebAssembly binary. For example:

package main

import (
	"embed"
	wasm "github.com/whosonfirst/go-whosonfirst-export-wasm/http"
	"log"
	"net/http"
)

//go:embed index.html example.*
var FS embed.FS

func main() {

	mux := http.NewServeMux()

	wasm.AppendAssetHandlers(mux)

	http_fs := http.FS(FS)
	example_handler := http.FileServer(http_fs)

	wasm_opts := wasm.DefaultWASMOptions()
	wasm_opts.EnableWASMExec()

	example_handler = wasm.AppendResourcesHandler(example_handler, wasm_opts)

	mux.Handle("/", example_handler)

	addr := "localhost:8080"
	log.Printf("Listening for requests on %s\n", addr)

	http.ListenAndServe(addr, mux)
}

Error handling omitted for brevity.

There is a full working example of this application in the cmd/example folder. To run this application type the following command:

$> go run -mod vendor cmd/example/main.go

Then if you visit http://localhost:8080 in your web browser you'll see something like this:

And when you click the Export button you'll see something like this:

The logic for the example application is defined in cmd/example/example.init.js.

See also

• https://github.com/whosonfirst/go-whosonfirst-export