Skip to content
Run WASM tests inside your browser
Branch: master
Clone or download
agnivade Update README
Add a note on taking CPU profiles
Latest commit 8c06ab2 Jul 14, 2019

wasmbrowsertest Build Status

Run Go wasm tests easily in your browser.

If you have a codebase targeting the wasm platform, chances are you would want to test your code in a browser. Currently, that process is a bit cumbersome:

  • The test needs to be compiled to a wasm file.
  • Then loaded into an HTML file along with the wasm_exec.js.
  • And finally, this needs to be served with a static file server and then loaded in the browser.

This tool automates all of that. So you just have to type GOOS=js GOARCH=wasm go test, and it automatically executes the tests inside a browser !


  • go get This will place the binary in $GOPATH/bin, or $GOBIN, if that has a different value.
  • Rename the binary to go_js_wasm_exec.
  • Add $GOBIN to $PATH if it is not already done.
  • Run tests as usual: GOOS=js GOARCH=wasm go test.
  • You can also take a cpu profile. Set the -cpuprofile flag for that.

Ok, but how does the magic work ?

go test allows invocation of a different binary to run a test. go help test has a line:

-exec xprog
	    Run the test binary using xprog. The behavior is the same as
	    in 'go run'. See 'go help run' for details.

And go help run says:

By default, 'go run' runs the compiled binary directly: 'a.out arguments...'.
If the -exec flag is given, 'go run' invokes the binary using xprog:
	'xprog a.out arguments...'.
If the -exec flag is not given, GOOS or GOARCH is different from the system
default, and a program named go_$GOOS_$GOARCH_exec can be found
on the current search path, 'go run' invokes the binary using that program,
for example 'go_nacl_386_exec a.out arguments...'. This allows execution of
cross-compiled programs when a simulator or other execution method is

So essentially, there are 2 ways:

  • Either have a binary with the name of go_js_wasm_exec in your $PATH.
  • Or set the -exec flag in your tests.

Use whatever works for you.

How is a CPU profile taken ?

A CPU profile is run during the duration of the test, and then converted to the pprof format so that it can be natively analyzed with the Go toolchain.

If I have a wasm binary file, can this run it in the browser ?

Yep. Just pass the wasm file as the first argument - wasmbrowsertest test.wasm.

Can I use this inside Travis ?


Add these lines to your .travis.yml

  chrome: stable

- go get
- mv $GOPATH/bin/wasmbrowsertest $GOPATH/bin/go_js_wasm_exec
- export PATH=$GOPATH/bin:$PATH

Now, just setting GOOS=js GOARCH=wasm will run your tests using wasmbrowsertest. For other CI environments, you have to do something similar.

What sorts of browsers are supported ?

This tool uses the ChromeDP protocol to run the tests inside a Chrome browser. So Chrome or any blink-based browser will work.

Why not firefox ?

Great question. The initial idea was to use a Selenium API and drive any browser to run the tests. But unfortunately, geckodriver does not support the ability to capture console logs - Hence, the shift to use the ChromeDP protocol circumvents the need to have any external driver binary and just have a browser installed in the machine.

You can’t perform that action at this time.