feat: TypeScript and ES6+ support using esbuild.

With the introduction of the "enhanced" compatibility mode, the test source code is transformed
using esbuild instead of Babel.

Source files with the extension ".ts" are loaded by esbuild's TypeScript loader, which results in partial
TypeScript support. This esbuild removes exactly the type information, but does not provide type safety.

Source files other than ".ts" are loaded by esbuild's JavaScript loader, which results in the support of a
more modern JavaScript dialect than goja.

cmd/runtime_options.go

@@ -23,10 +23,11 @@ func runtimeOptionFlagSet(includeSysEnv bool) *pflag.FlagSet {
 	flags.SortFlags = false
 	flags.Bool("include-system-env-vars", includeSysEnv, "pass the real system environment variables to the runtime")
 	flags.String("compatibility-mode", "extended",
-		`JavaScript compiler compatibility mode, "extended" or "base"
+		`JavaScript compiler compatibility mode, "extended" or "base" or "enhanced"
 base: pure goja - Golang JS VM supporting ES5.1+
 extended: base + Babel with parts of ES2015 preset
 		  slower to compile in case the script uses syntax unsupported by base
+enhanced: esbuild-based transpiling for TypeScript and ES6+ support
 `)
 	flags.StringP("type", "t", "", "override test type, \"js\" or \"archive\"")
 	flags.StringArrayP("env", "e", nil, "add/override environment variable with `VAR=value`")

cmd/runtime_options_test.go

@@ -109,6 +109,7 @@ func TestRuntimeOptions(t *testing.T) {
 		defaultCompatMode   = null.NewString("extended", false)
 		baseCompatMode      = null.NewString("base", true)
 		extendedCompatMode  = null.NewString("extended", true)
+		enhancedCompatMode  = null.NewString("enhanced", true)
 		defaultTracesOutput = null.NewString("none", false)
 	)
 
@@ -143,6 +144,16 @@ func TestRuntimeOptions(t *testing.T) {
 				TracesOutput:         defaultTracesOutput,
 			},
 		},
+		"disabled sys env by default with enhanced compat mode": {
+			useSysEnv: false,
+			systemEnv: map[string]string{"test1": "val1", "K6_COMPATIBILITY_MODE": "enhanced"},
+			expRTOpts: lib.RuntimeOptions{
+				IncludeSystemEnvVars: null.NewBool(false, false),
+				CompatibilityMode:    enhancedCompatMode,
+				Env:                  map[string]string{},
+				TracesOutput:         defaultTracesOutput,
+			},
+		},
 		"disabled sys env by cli 1": {
 			useSysEnv: true,
 			systemEnv: map[string]string{"test1": "val1", "K6_COMPATIBILITY_MODE": "base"},

examples/enhanced/script.ts

@@ -0,0 +1,6 @@
+import { User, newUser } from "./user.ts";
+
+export default () => {
+	const user: User = newUser("John");
+	console.log(user);
+};

examples/enhanced/user.ts

@@ -0,0 +1,20 @@
+interface User {
+	name: string;
+	id: number;
+}
+
+class UserAccount implements User {
+	name: string;
+	id: number;
+
+	constructor(name: string) {
+		this.name = name;
+		this.id = Math.floor(Math.random() * Number.MAX_SAFE_INTEGER);
+	}
+}
+
+function newUser(name: string): User {
+	return new UserAccount(name);
+}
+
+export { User, newUser };

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/Soontao/goHttpDigestClient v0.0.0-20170320082612-6d28bb1415c5
 	github.com/andybalholm/brotli v1.1.0
 	github.com/dop251/goja v0.0.0-20240220182346-e401ed450204
+	github.com/evanw/esbuild v0.21.2
 	github.com/fatih/color v1.16.0
 	github.com/go-sourcemap/sourcemap v2.1.4+incompatible
 	github.com/golang/protobuf v1.5.4

go.sum

@@ -57,6 +57,8 @@ github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymF
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/evanw/esbuild v0.21.2 h1:CLplcGi794CfHLVmUbvVfTMKkykm+nyIHU8SU60KUTA=
+github.com/evanw/esbuild v0.21.2/go.mod h1:D2vIQZqV/vIf/VRHtViaUtViZmG7o+kKmlBfVQuRi48=
 github.com/fatih/color v1.16.0 h1:zmkK9Ngbjj+K0yRhTVONQh1p/HknKYSlNT+vZCzyokM=
 github.com/fatih/color v1.16.0/go.mod h1:fL2Sau1YI5c0pdGEVCbKQbLXB6edEj1ZgiY4NijnWvE=
 github.com/fsnotify/fsnotify v1.5.4 h1:jRbGcIw6P2Meqdwuo0H1p6JVLbL5DHKAKlYndzMwVZI=

js/bundle_test.go

@@ -159,7 +159,7 @@ func TestNewBundle(t *testing.T) {
 			}{
 				{
 					"InvalidCompat", "es1", `export default function() {};`,
-					`invalid compatibility mode "es1". Use: "extended", "base"`,
+					`invalid compatibility mode "es1". Use: "extended", "base", "enhanced"`,
 				},
 				// ES2015 modules are not supported
 				{

js/compiler/compiler.go

@@ -239,19 +239,29 @@ func (c *Compiler) compileImpl(
 		c.logger.WithError(state.srcMapError).Warnf("Couldn't load source map for %s", filename)
 		ast, err = parser.ParseFile(nil, filename, code, 0, parser.WithDisableSourceMaps)
 	}
-	if err != nil {
-		if compatibilityMode == lib.CompatibilityModeExtended {
-			code, state.srcMap, err = c.Transform(src, filename, state.srcMap)
-			if err != nil {
-				return nil, code, err
-			}
-			// the compatibility mode "decreases" here as we shouldn't transform twice
-			return c.compileImpl(code, filename, wrap, lib.CompatibilityModeBase, state.srcMap)
+
+	if err == nil {
+		pgm, err := goja.CompileAST(ast, c.Options.Strict)
+		return pgm, code, err
+	}
+
+	if compatibilityMode == lib.CompatibilityModeExtended {
+		code, state.srcMap, err = c.Transform(src, filename, state.srcMap)
+		if err != nil {
+			return nil, code, err
+		}
+		// the compatibility mode "decreases" here as we shouldn't transform twice
+		return c.compileImpl(code, filename, wrap, lib.CompatibilityModeBase, state.srcMap)
+	}
+
+	if compatibilityMode == lib.CompatibilityModeEnhanced {
+		code, state.srcMap, err = esbuildTransform(src, filename)
+		if err != nil {
+			return nil, code, err
 		}
-		return nil, code, err
+		return c.compileImpl(code, filename, wrap, lib.CompatibilityModeBase, state.srcMap)
 	}
-	pgm, err := goja.CompileAST(ast, c.Options.Strict)
-	return pgm, code, err
+	return nil, code, err
 }
 
 type babel struct {

js/compiler/enhanced.go

@@ -0,0 +1,55 @@
+package compiler
+
+import (
+	"path/filepath"
+
+	"github.com/dop251/goja/file"
+	"github.com/dop251/goja/parser"
+	"github.com/evanw/esbuild/pkg/api"
+)
+
+func esbuildTransform(src, filename string) (code string, srcMap []byte, err error) {
+	opts := api.TransformOptions{
+		Sourcefile:     filename,
+		Loader:         api.LoaderJS,
+		Target:         api.ES2017,
+		Format:         api.FormatCommonJS,
+		Sourcemap:      api.SourceMapExternal,
+		SourcesContent: api.SourcesContentExclude,
+		LegalComments:  api.LegalCommentsNone,
+		Platform:       api.PlatformNeutral,
+		LogLevel:       api.LogLevelSilent,
+		Charset:        api.CharsetUTF8,
+	}
+
+	if filepath.Ext(filename) == ".ts" {
+		opts.Loader = api.LoaderTS
+	}
+
+	result := api.Transform(src, opts)
+
+	if hasError, err := esbuildCheckError(&result); hasError {
+		return "", nil, err
+	}
+
+	return string(result.Code), result.Map, nil
+}
+
+func esbuildCheckError(result *api.TransformResult) (bool, error) {
+	if len(result.Errors) == 0 {
+		return false, nil
+	}
+
+	msg := result.Errors[0]
+	err := &parser.Error{Message: msg.Text}
+
+	if msg.Location != nil {
+		err.Position = file.Position{
+			Filename: msg.Location.File,
+			Line:     msg.Location.Line,
+			Column:   msg.Location.Column,
+		}
+	}
+
+	return true, err
+}

js/compiler/enhanced_test.go

@@ -0,0 +1,50 @@
+package compiler
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/dop251/goja/parser"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_esbuildTransform_js(t *testing.T) {
+	t.Parallel()
+
+	code, srcMap, err := esbuildTransform(`export default function(name) { return "Hello, " + name }`, "script.js")
+
+	require.NoError(t, err)
+	require.NotNil(t, srcMap)
+	require.NotEmpty(t, code)
+}
+
+func Test_esbuildTransform_ts(t *testing.T) {
+	t.Parallel()
+
+	script := `export function hello(name:string) : string { return "Hello, " + name}`
+
+	code, srcMap, err := esbuildTransform(script, "script.ts")
+
+	require.NoError(t, err)
+	require.NotNil(t, srcMap)
+	require.NotEmpty(t, code)
+}
+
+func Test_esbuildTransform_error(t *testing.T) {
+	t.Parallel()
+
+	script := `export function hello(name:string) : string { return "Hello, " + name}`
+
+	_, _, err := esbuildTransform(script, "script.js")
+
+	require.Error(t, err)
+
+	var perr *parser.Error
+
+	require.True(t, errors.As(err, &perr))
+	require.NotNil(t, perr.Position)
+	require.Equal(t, "script.js", perr.Position.Filename)
+	require.Equal(t, 1, perr.Position.Line)
+	require.Equal(t, 26, perr.Position.Column)
+	require.Equal(t, "Expected \")\" but found \":\"", perr.Message)
+}

lib/runtime_options.go

@@ -17,6 +17,8 @@ const (
 	CompatibilityModeExtended CompatibilityMode = iota + 1
 	// CompatibilityModeBase is standard goja ES5.1+
 	CompatibilityModeBase
+	// CompatibilityModeEnhanced achieves TypeScript and ES6+ compatibility with esbuild
+	CompatibilityModeEnhanced
 )
 
 // RuntimeOptions are settings passed onto the goja JS runtime