GopherJS compiles Go code (go.dev) 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.
โคด๏ธ Help us make better decisions by filling a quick 15-question GopherJS user survey.- ๐ข Report and discuss issues.
- ๐ Share your knowledge and experience through articles and documentation.
- ๐ ๏ธ Write GopherJS bindings for other libraries or contribute to GopherJS itself.
- 2024-02-24: Go 1.19 support is available!
- 2022-08-18: 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! ๐ ๐ ๐
Give GopherJS a try on the GopherJS Playground.
Nearly everything, including Goroutines (compatibility documentation). Performance is quite good in most cases, see HTML5 game engine benchmark. Cgo is not supported.
GopherJS requires Go 1.19 or newer. If you need an older Go version, you can use an older GopherJS release.
Install GopherJS with go install
:
go install github.com/gopherjs/[email protected] # Or replace 'v1.19.0-beta1' with another version.
If your local Go distribution as reported by go version
is newer than Go 1.19, then you need to set the GOPHERJS_GOROOT
environment variable to a directory that contains a Go 1.19 distribution. For example:
go install golang.org/dl/go1.19.13@latest
go1.19.13 download
export GOPHERJS_GOROOT="$(go1.19.13 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.
If you want to use gopherjs run
or gopherjs test
to run the generated code locally, install Node.js 18 (or newer).
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
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.
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 valueGOPHERJS_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.
- Use the
-m
command line flag to generate minified code. - Apply gzip compression (https://en.wikipedia.org/wiki/HTTP_compression).
- Use
int
instead of(u)int8/16/32/64
. - Use
float64
instead offloat32
.
- #gopherjs Channel on Gophers Slack (invites to Gophers Slack are available here)
- Bindings to JavaScript APIs and libraries
- GopherJS Blog
- GopherJS on Twitter
- Examples, tutorials and blogs
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.
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.
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 GOOS
value of this environment is js
, and the GOARCH
value is ecmascript
. You may use these values in build constraints when writing platform-specific code. (GopherJS 1.17 and older used js
as the GOARCH
value.)
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 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.
If you're looking to make changes to the GopherJS compiler, see Developer Guidelines for additional developer information.