README
¶
gorunwasm -- an HTTP Server Wrapper For Go
Demo
<!doctype html>
<title>Go WASM Hello World</title>
<body>
<div>
<label for="who">Who are you?</label>
<input id="who" type="text" size="20">
</div>
<div id="output">...</div>
<script src="wasm_exec.js"></script>
<script src="index.js" data-input="#who" data-output="#output"></script>
</body>
// +build js
package main
import (
"fmt"
"os"
"syscall/js"
)
var document = js.Global().Get("document")
func main() {
input := document.Call("querySelector", os.Getenv("input"))
output := document.Call("querySelector", os.Getenv("output"))
input.Call("addEventListener", "change", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
val := input.Get("value")
output.Set("innerText", fmt.Sprintf("Hello %q", val))
return nil
}))
select {}
}
Then just gorunwasm within the folder containing those two files:
$ go get github.com/jcorbin/gorunwasm
$ gorunwasm
2019/05/27 19:14:53 Serving http files from "/Users/joshua/gorunwasm/hello"
2019/05/27 19:14:53 listening on http://127.0.0.1:58241
Open the browser, and type in the input:
But the real joy comes during development, let's break it:
diff --git a/main.go b/main.go
index 58886f6..956b143 100644
--- a/hello/main.go
+++ b/hello/main.go
@@ -24,7 +24,7 @@ func main() {
input.Call("addEventListener", "change", js.FuncOf(func(this js.Value, args []js.Value) interf
val := input.Get("value")
output.Set("innerText", fmt.Sprintf("Hello %q", val))
- return nil
+ // return nil FIXME oops
}))
select {}
See the syscall/js package and the golang WebAssembly
wiki for more.
HTML
You may write an index.html file within your main package, which will cause
gorunwasm to host an http.FileServer out of the main package directory,
rather than providing a static default index.html.
Any custom index.html:
- MUST include
<script src="wasm_exec.js"></script>-- hosted from$GOROOT/misc/wasm/wasm_exec.js, and is part of the upstream wasm runtime. - SHOULD include
<script src="index.js"></script>-- isgorunwasm's runtime harness, which can be further customized with data attributes:data-argsprovides JSON-encoded command line arguments, and causes the wasm program to be immediately ran after compilation.data-argv0provides an alternate program name to run the Go program as; the default is "PACKAGENAME.wasm".data-hrefprovides an alternate URL to thebuild.jsonconfig endpoint.- any other data attributes are passed as environment variables to the Go
program; access them the normal way with
os.Getenv("name")
Documentation
¶
Overview ¶
Package main implements the gorunwasm command, which runs an http server around a dynamic wasm building handler, along side a DOM-integrated runner script.
It hosts /wasm_exec.js as shipped with $GOROOT to implement the core Go class in the browser.
It hosts the wasm handler at /main.wasm.
It hosts a static /index.html wrapper which combines these, or an http.FileServer around the target package directory if it contains an index.html.
The runner script supports passing environment variables to the built Go wasm/js program:
<!doctype html> <title>Go WASM Hello World</title> <body> <div> <label for="who">Who are you?</label> <input id="who" type="text" size="20"> </div> <div id="output">...</div> <script src="wasm_exec.js"></script> <script src="index.js" data-input="#who" data-output="#output"></script> </body>
Which can then be used along side a corresponding main.go:
// +build js
package main
import (
"fmt"
"os"
"syscall/js"
)
var document = js.Global().Get("document")
func main() {
input := document.Call("querySelector", os.Getenv("input"))
output := document.Call("querySelector", os.Getenv("output"))
input.Call("addEventListener", "change", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
val := input.Get("value")
output.Set("innerText", fmt.Sprintf("Hello %q", val))
return nil
}))
select {}
}
The runner script also supports setting data-argv0 and data-args attributes to pass command line arguments. However environment variables are easier and less error prone to use, since they are simple key/value passing, where-as the args value must be a JSON encoded array of strings.
The runner script displays any text/plain content by replacing all body content with it. This aligns with WASMHandler redirecting to the build log on build failure.
Source Files
Directories