Top level await

js/bundle.go

@@ -331,9 +331,10 @@ func (b *Bundle) instantiate(vuImpl *moduleVUImpl, vuID uint64) (*BundleInstance
 		env:          b.preInitState.RuntimeOptions.Env,
 		moduleVUImpl: vuImpl,
 	}
+	var result *modules.RunSourceDataResult
 	callback := func() error { // this exists so that Sobek catches uncatchable panics such as Interrupt
 		var err error
-		bi.mainModule, err = modSys.RunSourceData(b.sourceData)
+		result, err = modSys.RunSourceData(b.sourceData)
 		return err
 	}
 
@@ -346,6 +347,14 @@ func (b *Bundle) instantiate(vuImpl *moduleVUImpl, vuID uint64) (*BundleInstance
 
 	<-initDone
 
+	if err == nil {
+		var finished bool
+		bi.mainModule, finished, err = result.Result()
+		if !finished {
+			return nil, errors.New("initializing the main module hasn't finished, this is a bug in k6 please report it")
+		}
+	}
+
 	if err != nil {
 		var exception *sobek.Exception
 		if errors.As(err, &exception) {

js/bundle_test.go

@@ -126,7 +126,7 @@ func TestNewBundle(t *testing.T) {
 	t.Run("InvalidExports", func(t *testing.T) {
 		t.Parallel()
 		_, err := getSimpleBundle(t, "/script.js", `module.exports = null`)
-		require.EqualError(t, err, "GoError: CommonJS's exports must not be null\n") // TODO: try to remove the GoError from herer
+		require.EqualError(t, err, "CommonJS's exports must not be null")
 	})
 	t.Run("DefaultUndefined", func(t *testing.T) {
 		t.Parallel()
@@ -983,3 +983,18 @@ func TestGlobalTimers(t *testing.T) {
 		})
 	}
 }
+
+func TestTopLevelAwaitErrors(t *testing.T) {
+	t.Parallel()
+	data := `
+		const delay = (delayInms) => {
+			return new Promise(resolve => setTimeout(resolve, delayInms));
+		}
+
+		await delay(10).then(() => {something});
+		export default () => {}
+	`
+
+	_, err := getSimpleBundle(t, "/script.js", data)
+	require.ErrorContains(t, err, "ReferenceError: something is not defined")
+}

js/modules/require_impl.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/grafana/sobek"
+
 	"go.k6.io/k6/loader"
 )
 
@@ -47,6 +48,7 @@ func (ms *ModuleSystem) Require(specifier string) (*sobek.Object, error) {
 	} else {
 		panic(fmt.Sprintf("expected sobek.CyclicModuleRecord, but for some reason got a %T", m))
 	}
+	promisesThenIgnore(rt, promise)
 	switch promise.State() {
 	case sobek.PromiseStateRejected:
 		err = promise.Result().Export().(error) //nolint:forcetypeassert
@@ -195,3 +197,11 @@ func getPreviousRequiringFile(vu VU) (string, error) {
 	}
 	return result, nil
 }
+
+// sets the provided promise in such way as to ignore falures
+// this is mostly needed as failures are handled separately and we do not want those to lead to stopping the event loop
+func promisesThenIgnore(rt *sobek.Runtime, promise *sobek.Promise) {
+	cal, _ := sobek.AssertFunction(rt.ToValue(promise).ToObject(rt).Get("then"))
+	handler := rt.ToValue(func(_ sobek.Value) {})
+	_, _ = cal(rt.ToValue(promise), handler, handler)
+}

js/modules/resolution.go

@@ -233,10 +233,7 @@ func NewModuleSystem(resolver *ModuleResolver, vu VU) *ModuleSystem {
 // RunSourceData runs the provided sourceData and adds it to the cache.
 // If a module with the same specifier as the source is already cached
 // it will be used instead of reevaluating the source from the provided SourceData.
-//
-// TODO: this API will likely change as native ESM support will likely not let us have the exports
-// as one big sobek.Value that we can manipulate
-func (ms *ModuleSystem) RunSourceData(source *loader.SourceData) (sobek.ModuleRecord, error) {
+func (ms *ModuleSystem) RunSourceData(source *loader.SourceData) (*RunSourceDataResult, error) {
 	specifier := source.URL.String()
 	pwd := source.URL.JoinPath("../")
 	if _, err := ms.resolver.resolveLoaded(pwd, specifier, source.Data); err != nil {
@@ -256,14 +253,32 @@ func (ms *ModuleSystem) RunSourceData(source *loader.SourceData) (sobek.ModuleRe
 	}
 	rt := ms.vu.Runtime()
 	promise := rt.CyclicModuleRecordEvaluate(ci, ms.resolver.sobekModuleResolver)
-	switch promise.State() {
+
+	promisesThenIgnore(rt, promise)
+
+	return &RunSourceDataResult{
+		promise: promise,
+		mod:     mod,
+	}, nil
+}
+
+// RunSourceDataResult helps with the asynchronous nature of ESM
+// it wraps the promise that is returned from Sobek while at the same time allowing access to the module record
+type RunSourceDataResult struct {
+	promise *sobek.Promise
+	mod     sobek.ModuleRecord
+}
+
+// Result returns either the underlying module or error if the promise has been completed and true,
+// or false if the promise still hasn't been completed
+func (r *RunSourceDataResult) Result() (sobek.ModuleRecord, bool, error) {
+	switch r.promise.State() {
 	case sobek.PromiseStateRejected:
-		return nil, promise.Result().Export().(error) //nolint:forcetypeassert
+		return nil, true, r.promise.Result().Export().(error) //nolint:forcetypeassert
 	case sobek.PromiseStateFulfilled:
-		return mod, nil
+		return r.mod, true, nil
 	default:
-		// TODO(@mstoykov): this will require having some callbacks through the code, but should be doable, just not pretty
-		panic("TLA not supported in k6 at the moment")
+		return nil, false, nil
 	}
 }
 

js/tc39/breaking_test_errors-experimental_enhanced.json

@@ -82,6 +82,8 @@
   "test/language/module-code/instn-star-err-not-found.js-strict:true": "test/language/module-code/instn-star-err-not-found.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/module-code/parse-err-hoist-lex-fun.js-strict:true": "test/language/module-code/parse-err-hoist-lex-fun.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/module-code/parse-err-return.js-strict:true": "test/language/module-code/parse-err-return.js: error is not an object (Test262: This statement should not be evaluated.)",
+  "test/language/module-code/top-level-await/new-await.js-strict:true": "test/language/module-code/top-level-await/new-await.js: error is not an object (Test262: This statement should not be evaluated.)",
+  "test/language/module-code/top-level-await/no-operand.js-strict:true": "test/language/module-code/top-level-await/no-operand.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/reserved-words/await-module.js-strict:true": "test/language/reserved-words/await-module.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/statements/class/class-name-ident-await-escaped-module.js-strict:true": "test/language/statements/class/class-name-ident-await-escaped-module.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/statements/class/class-name-ident-await-module.js-strict:true": "test/language/statements/class/class-name-ident-await-module.js: error is not an object (Test262: This statement should not be evaluated.)",

js/tc39/breaking_test_errors-extended.json

@@ -82,6 +82,8 @@
   "test/language/module-code/instn-star-err-not-found.js-strict:true": "test/language/module-code/instn-star-err-not-found.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/module-code/parse-err-hoist-lex-fun.js-strict:true": "test/language/module-code/parse-err-hoist-lex-fun.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/module-code/parse-err-return.js-strict:true": "test/language/module-code/parse-err-return.js: error is not an object (Test262: This statement should not be evaluated.)",
+  "test/language/module-code/top-level-await/new-await.js-strict:true": "test/language/module-code/top-level-await/new-await.js: error is not an object (Test262: This statement should not be evaluated.)",
+  "test/language/module-code/top-level-await/no-operand.js-strict:true": "test/language/module-code/top-level-await/no-operand.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/reserved-words/await-module.js-strict:true": "test/language/reserved-words/await-module.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/statements/class/class-name-ident-await-escaped-module.js-strict:true": "test/language/statements/class/class-name-ident-await-escaped-module.js: error is not an object (Test262: This statement should not be evaluated.)",
   "test/language/statements/class/class-name-ident-await-module.js-strict:true": "test/language/statements/class/class-name-ident-await-module.js: error is not an object (Test262: This statement should not be evaluated.)",

js/tc39/tc39_test.go

@@ -56,8 +56,8 @@ var (
 	featuresBlockList = []string{
 		"IsHTMLDDA",                   // not supported at all
 		"async-iteration",             // not supported at all
-		"top-level-await",             // not supported at all
 		"String.prototype.replaceAll", // not supported at all, Stage 4 since 2020
+		"dynamic-import",              // not support in k6
 
 		// from Sobek
 		"Symbol.asyncIterator",
@@ -737,10 +737,17 @@ func (ctx *tc39TestCtx) runTC39Module(name, src string, includes []string, vm *s
 	moduleRuntime.VU.InitEnvField.CWD = base
 
 	early = false
-	_, err = ms.RunSourceData(&loader.SourceData{
+	result, err := ms.RunSourceData(&loader.SourceData{
 		Data: []byte(src),
 		URL:  u,
 	})
+	if err == nil {
+		var finished bool
+		_, finished, err = result.Result()
+		if !finished {
+			panic("tc39 has no tests where this should happen")
+		}
+	}
 
 	return early, err
 }