GopherJS - A compiler from Go to JavaScript
GopherJS compiles Go code (golang.org) to pure JavaScript code. Its main purpose is to give you the opportunity to write front-end code in Go which will still run in all browsers.
Help us make GopherJS better!
What's new?
- 2022-XX-XX: Go 1.18 support is available
- 2021-09-19: Go 1.17 support is available!
- 2021-08-23: Go Modules are now fully supported.
- 2021-06-19: Complete
syscall/js
package implementation compatible with the upstream Go 1.16.
- 2021-04-04: Go 1.16 is now officially supported! 🎉 🎉 🎉
Playground
Give GopherJS a try on the GopherJS Playground.
What is supported?
Nearly everything, including Goroutines (compatibility documentation). Performance is quite good in most cases, see HTML5 game engine benchmark. Cgo is not supported.
Installation and Usage
GopherJS requires Go 1.18 or newer. If you need an older Go
version, you can use an older Gopher release.
Get or update GopherJS and dependencies with:
go get -u github.com/gopherjs/gopherjs
If your local Go distribution as reported by go version
is newer than Go 1.18, then you need to set the GOPHERJS_GOROOT
environment variable to a directory that contains a Go 1.18 distribution. For example:
go get golang.org/dl/go1.18.1
go1.18.1 download
export GOPHERJS_GOROOT="$(go1.18.1 env GOROOT)" # Also add this line to your .profile or equivalent.
Now you can use gopherjs build [package]
, gopherjs build [files]
or gopherjs install [package]
which behave similar to the go
tool. For main
packages, these commands create a .js
file and .js.map
source map in the current directory or in $GOPATH/bin
. The generated JavaScript file can be used as usual in a website. Use gopherjs help [command]
to get a list of possible command line flags, e.g. for minification and automatically watching for changes.
gopherjs
uses your platform's default GOOS
value when generating code. Supported GOOS
values are: linux
, darwin
. If you're on a different platform (e.g., Windows or FreeBSD), you'll need to set the GOOS
environment variable to a supported value. For example, GOOS=linux gopherjs build [package]
.
Note: GopherJS will try to write compiled object files of the core packages to your $GOROOT/pkg directory. If that fails, it will fall back to $GOPATH/pkg.
gopherjs run, gopherjs test
If you want to use gopherjs run
or gopherjs test
to run the generated code locally, install Node.js 10.0.0 (or newer), and the source-map-support
module:
npm install --global source-map-support
On supported GOOS
platforms, it's possible to make system calls (file system access, etc.) available. See doc/syscalls.md for instructions on how to do so.
gopherjs serve
gopherjs serve
is a useful command you can use during development. It will start an HTTP server serving on ":8080" by default, then dynamically compile your Go packages with GopherJS and serve them.
For example, navigating to http://localhost:8080/example.com/user/project/
should compile and run the Go package example.com/user/project
. The generated JavaScript output will be served at http://localhost:8080/example.com/user/project/project.js
(the .js file name will be equal to the base directory name). If the directory contains index.html
it will be served, otherwise a minimal index.html
that includes <script src="project.js"></script>
will be provided, causing the JavaScript to be executed. All other static files will be served too.
Refreshing in the browser will rebuild the served files if needed. Compilation errors will be displayed in terminal, and in browser console. Additionally, it will serve $GOROOT and $GOPATH for sourcemaps.
If you include an argument, it will be the root from which everything is served. For example, if you run gopherjs serve github.com/user/project
then the generated JavaScript for the package github.com/user/project/mypkg will be served at http://localhost:8080/mypkg/mypkg.js.
Environment Variables
There are some GopherJS-specific environment variables:
GOPHERJS_GOROOT
- if set, GopherJS uses this value as the default GOROOT
value, instead of using the system GOROOT as the default GOROOT value
GOPHERJS_SKIP_VERSION_CHECK
- if set to true, GopherJS will not check
Go version in the GOROOT for compatibility with the GopherJS release. This
is primarily useful for testing GopherJS against unreleased versions of Go.
Getting started
Interacting with the DOM
The package github.com/gopherjs/gopherjs/js
(see documentation) provides functions for interacting with native JavaScript APIs. For example the line
document.write("Hello world!");
would look like this in Go:
js.Global.Get("document").Call("write", "Hello world!")
You may also want use the DOM bindings, the jQuery bindings (see TodoMVC Example) or the AngularJS bindings. Those are some of the bindings to JavaScript APIs and libraries by community members.
Providing library functions for use in other JavaScript code
Set a global variable to a map that contains the functions:
package main
import "github.com/gopherjs/gopherjs/js"
func main() {
js.Global.Set("pet", map[string]interface{}{
"New": New,
})
}
type Pet struct {
name string
}
func New(name string) *js.Object {
return js.MakeWrapper(&Pet{name})
}
func (p *Pet) Name() string {
return p.name
}
func (p *Pet) SetName(name string) {
p.name = name
}
For more details see Jason Stone's blog post about GopherJS.
Architecture
General
GopherJS emulates a 32-bit environment. This means that int
, uint
and uintptr
have a precision of 32 bits. However, the explicit 64-bit integer types int64
and uint64
are supported. The GOARCH
value of GopherJS is "js". You may use it as a build constraint: // +build js,-wasm
.
Application Lifecycle
The main
function is executed as usual after all init
functions have run. JavaScript callbacks can also invoke Go functions, even after the main
function has exited. Therefore the end of the main
function should not be regarded as the end of the application and does not end the execution of other goroutines.
In the browser, calling os.Exit
(e.g. indirectly by log.Fatal
) also does not terminate the execution of the program. For convenience, it calls runtime.Goexit
to immediately terminate the calling goroutine.
Goroutines
Goroutines are fully supported by GopherJS. The only restriction is that you need to start a new goroutine if you want to use blocking code called from external JavaScript:
js.Global.Get("myButton").Call("addEventListener", "click", func() {
go func() {
[...]
someBlockingFunction()
[...]
}()
})
How it works:
JavaScript has no concept of concurrency (except web workers, but those are too strictly separated to be used for goroutines). Because of that, instructions in JavaScript are never blocking. A blocking call would effectively freeze the responsiveness of your web page, so calls with callback arguments are used instead.
GopherJS does some heavy lifting to work around this restriction: Whenever an instruction is blocking (e.g. communicating with a channel that isn't ready), the whole stack will unwind (= all functions return) and the goroutine will be put to sleep. Then another goroutine which is ready to resume gets picked and its stack with all local variables will be restored.
GopherJS Development
If you're looking to make changes to the GopherJS compiler, see Developer Guidelines for additional developer information.