fix #281: --out-extension for custom extensions

CHANGELOG.md

@@ -16,6 +16,10 @@
 
     When the `tsconfig.json` settings have been force-overridden using the new `--tsconfig` flag, the path resolution behavior behaved subtly differently than if esbuild naturally discovers the `tsconfig.json` file without the flag. The difference caused package paths present in a `node_modules` folder to incorrectly take precedence over custom path aliases configured in `tsconfig.json`. The ordering has been corrected such that custom path aliases always take place over `node_modules`.
 
+* Add the `--out-extension` flag for custom output extensions ([#281](https://github.com/evanw/esbuild/issues/281))
+
+    Previously esbuild could only output files ending in `.js`. Now you can override this to another extension by passing something like `--out-extension:.js=.mjs`. This allows generating output files with the node-specific `.cjs` and `.mjs` extensions without having to use a separate command to rename them afterwards.
+
 ## 0.6.5
 
 * Fix IIFE wrapper for ES5

README.md

@@ -383,6 +383,7 @@ Advanced options:
   --strict                  Transforms handle edge cases but have more overhead
   --pure=N                  Mark the name N as a pure function for tree shaking
   --tsconfig=...            Use this tsconfig.json file instead of other ones
+  --out-extension:.js=.mjs  Use a custom output extension instead of ".js"
 
 Examples:
   # Produces dist/entry_point.js and dist/entry_point.js.map

cmd/esbuild/main.go

@@ -54,6 +54,7 @@ Advanced options:
   --strict                  Transforms handle edge cases but have more overhead
   --pure=N                  Mark the name N as a pure function for tree shaking
   --tsconfig=...            Use this tsconfig.json file instead of other ones
+  --out-extension:.js=.mjs  Use a custom output extension instead of ".js"
 
 Examples:
   # Produces dist/entry_point.js and dist/entry_point.js.map

internal/bundler/bundler_test.go

@@ -4659,3 +4659,45 @@ func TestIIFE_ES5(t *testing.T) {
 		},
 	})
 }
+
+func TestOutputExtensionRemappingFile(t *testing.T) {
+	expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				console.log('test');
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			IsBundling:       true,
+			OutputExtensions: map[string]string{".js": ".notjs"},
+			AbsOutputFile:    "/out.js",
+		},
+		expected: map[string]string{
+			"/out.js": `// /entry.js
+console.log("test");
+`,
+		},
+	})
+}
+
+func TestOutputExtensionRemappingDir(t *testing.T) {
+	expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				console.log('test');
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			IsBundling:       true,
+			OutputExtensions: map[string]string{".js": ".notjs"},
+			AbsOutputDir:     "/out",
+		},
+		expected: map[string]string{
+			"/out/entry.notjs": `// /entry.js
+console.log("test");
+`,
+		},
+	})
+}

internal/bundler/linker.go

@@ -2077,9 +2077,7 @@ func (c *linkerContext) computeChunks() []chunkMeta {
 
 			// Swap the extension for ".js"
 			ext := c.fs.Ext(chunkRelPath)
-			if ext != ".js" {
-				chunkRelPath = chunkRelPath[:len(chunkRelPath)-len(ext)] + ".js"
-			}
+			chunkRelPath = chunkRelPath[:len(chunkRelPath)-len(ext)] + c.options.OutputExtensionFor(".js")
 		}
 
 		// Always use cross-platform path separators to avoid problems with Windows
@@ -2128,7 +2126,7 @@ func (c *linkerContext) computeChunks() []chunkMeta {
 					bytes := []byte(lowerCaseAbsPathForWindows(chunk.relPath))
 					hashBytes := sha1.Sum(bytes)
 					hash := base64.URLEncoding.EncodeToString(hashBytes[:])[:8]
-					chunk.relPath = "chunk." + hash + ".js"
+					chunk.relPath = "chunk." + hash + c.options.OutputExtensionFor(".js")
 				}
 
 				chunk.entryBits = partMeta.entryBits

internal/config/config.go

@@ -152,6 +152,7 @@ type Options struct {
 
 	AbsOutputFile     string
 	AbsOutputDir      string
+	OutputExtensions  map[string]string
 	ModuleName        string
 	TsConfigOverride  string
 	ExtensionToLoader map[string]Loader
@@ -163,3 +164,10 @@ type Options struct {
 	SourceMap SourceMap
 	Stdin     *StdinInfo
 }
+
+func (options *Options) OutputExtensionFor(key string) string {
+	if ext, ok := options.OutputExtensions[key]; ok {
+		return ext
+	}
+	return key
+}

lib/common.ts

@@ -22,7 +22,12 @@ function pushCommonFlags(flags: string[], options: types.CommonOptions, isTTY: b
 
   if (options.jsxFactory) flags.push(`--jsx-factory=${options.jsxFactory}`);
   if (options.jsxFragment) flags.push(`--jsx-fragment=${options.jsxFragment}`);
-  if (options.define) for (let key in options.define) flags.push(`--define:${key}=${options.define[key]}`);
+  if (options.define) {
+    for (let key in options.define) {
+      if (key.indexOf('=') >= 0) throw new Error(`Invalid define: ${key}`);
+      flags.push(`--define:${key}=${options.define[key]}`);
+    }
+  }
   if (options.pure) for (let fn of options.pure) flags.push(`--pure:${fn}`);
 
   if (options.color) flags.push(`--color=${options.color}`);
@@ -49,7 +54,18 @@ function flagsForBuildOptions(options: types.BuildOptions, isTTY: boolean): [str
   if (options.tsconfig) flags.push(`--tsconfig=${options.tsconfig}`);
   if (options.resolveExtensions) flags.push(`--resolve-extensions=${options.resolveExtensions.join(',')}`);
   if (options.external) for (let name of options.external) flags.push(`--external:${name}`);
-  if (options.loader) for (let ext in options.loader) flags.push(`--loader:${ext}=${options.loader[ext]}`);
+  if (options.loader) {
+    for (let ext in options.loader) {
+      if (ext.indexOf('=') >= 0) throw new Error(`Invalid extension: ${ext}`);
+      flags.push(`--loader:${ext}=${options.loader[ext]}`);
+    }
+  }
+  if (options.outExtension) {
+    for (let ext in options.outExtension) {
+      if (ext.indexOf('=') >= 0) throw new Error(`Invalid extension: ${ext}`);
+      flags.push(`--out-extension:${ext}=${options.outExtension[ext]}`);
+    }
+  }
 
   if (options.entryPoints) {
     for (let entryPoint of options.entryPoints) {

lib/types.ts

@@ -39,6 +39,7 @@ export interface BuildOptions extends CommonOptions {
   resolveExtensions?: string[];
   write?: boolean;
   tsconfig?: string;
+  outExtension?: { [ext: string]: string };
 
   entryPoints?: string[];
   stdin?: StdinOptions;

pkg/api/api.go

@@ -217,6 +217,7 @@ type BuildOptions struct {
 	Loaders           map[string]Loader
 	ResolveExtensions []string
 	Tsconfig          string
+	OutExtensions     map[string]string
 
 	EntryPoints []string
 	Stdin       *StdinOptions

pkg/api/api_impl.go

@@ -216,12 +216,16 @@ func validateExternals(log logging.Log, fs fs.FS, paths []string) config.Externa
 	return result
 }
 
+func isValidExtension(ext string) bool {
+	return len(ext) >= 2 && ext[0] == '.' && ext[len(ext)-1] != '.'
+}
+
 func validateResolveExtensions(log logging.Log, order []string) []string {
 	if order == nil {
 		return []string{".tsx", ".ts", ".jsx", ".mjs", ".cjs", ".js", ".json"}
 	}
 	for _, ext := range order {
-		if len(ext) < 2 || ext[0] != '.' {
+		if !isValidExtension(ext) {
 			log.AddError(nil, ast.Loc{}, fmt.Sprintf("Invalid file extension: %q", ext))
 		}
 	}
@@ -232,7 +236,7 @@ func validateLoaders(log logging.Log, loaders map[string]Loader) map[string]conf
 	result := bundler.DefaultExtensionToLoaderMap()
 	if loaders != nil {
 		for ext, loader := range loaders {
-			if len(ext) < 2 || ext[0] != '.' || ext[len(ext)-1] == '.' {
+			if !isValidExtension(ext) {
 				log.AddError(nil, ast.Loc{}, fmt.Sprintf("Invalid file extension: %q", ext))
 			}
 			result[ext] = validateLoader(loader)
@@ -343,6 +347,20 @@ func validatePath(log logging.Log, fs fs.FS, relPath string) string {
 	return absPath
 }
 
+func validateOutputExtensions(log logging.Log, outExtensions map[string]string) map[string]string {
+	result := make(map[string]string)
+	for key, value := range outExtensions {
+		if key != ".js" {
+			log.AddError(nil, ast.Loc{}, fmt.Sprintf("Invalid output extension: %q (valid: .js)", key))
+		}
+		if !isValidExtension(value) {
+			log.AddError(nil, ast.Loc{}, fmt.Sprintf("Invalid output extension: %q", value))
+		}
+		result[key] = value
+	}
+	return result
+}
+
 func messagesOfKind(kind logging.MsgKind, msgs []logging.Msg) []Message {
 	var filtered []Message
 	for _, msg := range msgs {
@@ -407,6 +425,7 @@ func buildImpl(buildOpts BuildOptions) BuildResult {
 		AbsOutputFile:     validatePath(log, realFS, buildOpts.Outfile),
 		AbsOutputDir:      validatePath(log, realFS, buildOpts.Outdir),
 		AbsMetadataFile:   validatePath(log, realFS, buildOpts.Metafile),
+		OutputExtensions:  validateOutputExtensions(log, buildOpts.OutExtensions),
 		ExtensionToLoader: validateLoaders(log, buildOpts.Loaders),
 		ExtensionOrder:    validateResolveExtensions(log, buildOpts.ResolveExtensions),
 		ExternalModules:   validateExternals(log, realFS, buildOpts.Externals),

pkg/cli/cli_impl.go

@@ -185,6 +185,17 @@ func parseOptionsImpl(osArgs []string, buildOpts *api.BuildOptions, transformOpt
 				transformOpts.Engines = engines
 			}
 
+		case strings.HasPrefix(arg, "--out-extension:") && buildOpts != nil:
+			value := arg[len("--out-extension:"):]
+			equals := strings.IndexByte(value, '=')
+			if equals == -1 {
+				return fmt.Errorf("Missing \"=\": %q", value)
+			}
+			if buildOpts.OutExtensions == nil {
+				buildOpts.OutExtensions = make(map[string]string)
+			}
+			buildOpts.OutExtensions[value[:equals]] = value[equals+1:]
+
 		case arg == "--strict":
 			value := api.StrictOptions{
 				NullishCoalescing: true,