js: make certain only one copy of the exports is used per each module (…

…#2773)

This is inline with ESM and works for source code modules, but not for
modules written in go as the code was never made to work with it.

This also lets (as the test suggests) change what `k6/http`.get is
across the VU just as it should be possible.

js/initcontext.go

@@ -45,13 +45,14 @@ type InitContext struct {
 	pwd         *url.URL
 
 	// Cache of loaded programs and files.
-	programs map[string]programWithSource
+	programs     map[string]programWithSource
+	exportsCache map[string]goja.Value
 
 	compatibilityMode lib.CompatibilityMode
 
 	logger logrus.FieldLogger
 
-	modules map[string]interface{}
+	moduleRegistry map[string]interface{}
 }
 
 // NewInitContext creates a new initcontext with the provided arguments
@@ -66,7 +67,8 @@ func NewInitContext(
 		programs:          make(map[string]programWithSource),
 		compatibilityMode: compatMode,
 		logger:            logger,
-		modules:           getJSModules(),
+		moduleRegistry:    getJSModules(),
+		exportsCache:      make(map[string]goja.Value),
 		moduleVUImpl: &moduleVUImpl{
 			ctx:     context.Background(),
 			runtime: rt,
@@ -92,14 +94,20 @@ func newBoundInitContext(base *InitContext, vuImpl *moduleVUImpl) *InitContext {
 
 		programs:          programs,
 		compatibilityMode: base.compatibilityMode,
+		exportsCache:      make(map[string]goja.Value),
 		logger:            base.logger,
-		modules:           base.modules,
+		moduleRegistry:    base.moduleRegistry,
 		moduleVUImpl:      vuImpl,
 	}
 }
 
 // Require is called when a module/file needs to be loaded by a script
-func (i *InitContext) Require(arg string) goja.Value {
+func (i *InitContext) Require(arg string) (export goja.Value) {
+	var ok bool
+	if export, ok = i.exportsCache[arg]; ok {
+		return export
+	}
+	defer func() { i.exportsCache[arg] = export }()
 	switch {
 	case arg == "k6", strings.HasPrefix(arg, "k6/"):
 		// Builtin or external modules ("k6", "k6/*", or "k6/x/*") are handled
@@ -144,7 +152,7 @@ func toESModuleExports(exp modules.Exports) interface{} {
 }
 
 func (i *InitContext) requireModule(name string) (goja.Value, error) {
-	mod, ok := i.modules[name]
+	mod, ok := i.moduleRegistry[name]
 	if !ok {
 		return nil, fmt.Errorf("unknown module: %s", name)
 	}

js/initcontext_test.go

@@ -687,3 +687,34 @@ export default function () {
 	// likely settings in the transpilers
 	require.Equal(t, "cool is cool\n\tat webpack:///./test1.ts:2:4(2)\n\tat r (webpack:///./test1.ts:5:4(3))\n\tat file:///script.js:4:2(4)\n\tat native\n", exception.String())
 }
+
+func TestImportModificationsAreConsistentBetweenFiles(t *testing.T) {
+	t.Parallel()
+	logger := testutils.NewLogger(t)
+	fs := afero.NewMemMapFs()
+	require.NoError(t, afero.WriteFile(fs, "/notk6.js", []byte(`export default {group}; function group() {}`), 0o644))
+	require.NoError(t, afero.WriteFile(fs, "/instrument.js", []byte(`
+    import k6 from "k6";
+    k6.newKey = 5;
+    k6.group = 3;
+
+    import notk6 from "./notk6.js";
+    notk6.group = 3;
+    notk6.newKey = 5;
+    `), 0o644))
+
+	b, err := getSimpleBundle(t, "/script.js", `
+    import k6 from "k6";
+    import notk6 from "./notk6.js";
+    import "./instrument.js";
+    if (k6.newKey != 5) { throw "k6.newKey is wrong "+ k6.newKey}
+    if (k6.group != 3) { throw "k6.group is wrong "+ k6.group}
+    if (notk6.newKey != 5) { throw "notk6.newKey is wrong "+ notk6.newKey}
+    if (notk6.group != 3) { throw "notk6.group is wrong "+ notk6.group}
+    export default () => { throw "this shouldn't be ran" }
+`, fs)
+	require.NoError(t, err, "bundle error")
+
+	_, err = b.Instantiate(logger, 0)
+	require.NoError(t, err)
+}