Update extension to ModuleV2

This is done to move the extension to the new way of structuring JS
modules, and standardize how the main context and goja runtime are
accessed.

For background take a look at grafana/k6@34a7743fb,
grafana/k6#2108, and the "Advanced JavaScript
extension" section in
https://k6.io/docs/misc/k6-extensions/#writing-a-new-extension. The
tldr; is that this structure allows JS extensions to access internal k6
objects, is a saner alternative to `common.Bind()` (which we plan to
deprecate eventually), and has the wanted side effect that each VU gets
a separate instance of the module.

main.go

@@ -21,8 +21,6 @@
 package browser
 
 import (
-	"context"
-
 	"github.com/dop251/goja"
 	"github.com/grafana/xk6-browser/api"
 	"github.com/grafana/xk6-browser/chromium"
@@ -34,24 +32,55 @@ import (
 
 const version = "v0.1.0"
 
-// JSModule is the entrypoint into the browser JS module
-type JSModule struct {
-	// For when https://github.com/k6io/k6/issues/1802 is fixed
-	//Chromium api.BrowserType
-	Devices map[string]common.Device
-	Version string
+type (
+	// RootModule is the global module instance that will create module
+	// instances for each VU.
+	RootModule struct{}
+
+	// JSModule is the entrypoint into the browser JS module
+	JSModule struct {
+		k6modules.InstanceCore
+		Devices map[string]common.Device
+		Version string
+	}
+
+	// ModuleInstance represents an instance of the JS module.
+	ModuleInstance struct {
+		k6modules.InstanceCore
+		mod *JSModule
+	}
+)
+
+var (
+	_ k6modules.IsModuleV2 = &RootModule{}
+	_ k6modules.Instance   = &ModuleInstance{}
+)
+
+// New returns a pointer to a new RootModule instance.
+func New() *RootModule {
+	return &RootModule{}
 }
 
-// NewJSModule creates a new browser module
-func NewJSModule(version string) *JSModule {
-	return &JSModule{
-		//Chromium: chromium.NewBrowserType(),
-		Devices: common.GetDevices(),
-		Version: version,
+// NewModuleInstance implements the modules.IsModuleV2 interface to return
+// a new instance for each VU.
+func (*RootModule) NewModuleInstance(m k6modules.InstanceCore) k6modules.Instance {
+	return &ModuleInstance{
+		InstanceCore: m,
+		mod: &JSModule{
+			InstanceCore: m,
+			Devices:      common.GetDevices(),
+			Version:      version,
+		},
 	}
 }
 
-func (m *JSModule) Launch(ctx context.Context, browserName string, opts goja.Value) api.Browser {
+// GetExports returns the exports of the JS module so that it can be used in
+// test scripts.
+func (mi *ModuleInstance) GetExports() k6modules.Exports {
+	return k6modules.Exports{Default: mi.mod}
+}
+
+func (m *JSModule) Launch(browserName string, opts goja.Value) api.Browser {
 	/*go func() {
 		f, err := os.Create("./cpu.profile")
 		if err != nil {
@@ -63,15 +92,15 @@ func (m *JSModule) Launch(ctx context.Context, browserName string, opts goja.Val
 	}()*/
 
 	if browserName == "chromium" {
-		bt := chromium.NewBrowserType(ctx)
+		bt := chromium.NewBrowserType(m.GetContext())
 		return bt.Launch(opts)
 	}
 
-	rt := k6common.GetRuntime(ctx)
-	k6common.Throw(rt, errors.Errorf("Currently 'chromium' is the only supported browser"))
+	k6common.Throw(m.GetRuntime(),
+		errors.Errorf("Currently 'chromium' is the only supported browser"))
 	return nil
 }
 
 func init() {
-	k6modules.Register("k6/x/browser", NewJSModule(version))
+	k6modules.Register("k6/x/browser", New())
 }