feat: add ESM (.mjs) file support (#57)

resolves: #53

docs/core/usage.md

@@ -58,7 +58,7 @@ Where <code>[options]</code> are mostly optional configuration flags—see [Opti
 	<p>Log various story statistics.  Primarily, passage and word counts.</p>
 	<p role="note"><b>Note:</b> Unsupported when watch mode (<kbd>-w</kbd>, <kbd>--watch</kbd>) is enabled.</p>
 </dd>
-<dt><kbd>-m SRC</kbd>, <kbd>--module=SRC</kbd></dt><dd>Module sources (repeatable); may consist of supported files and/or directories to recursively search for such files.  Each file will be wrapped within the appropriate markup and bundled into the &lt;head&gt; element of the compiled HTML.  Supported files: <code>.css</code>, <code>.js</code>, <code>.otf</code>, <code>.ttf</code>, <code>.woff</code>, <code>.woff2</code>.</dd>
+<dt><kbd>-m SRC</kbd>, <kbd>--module=SRC</kbd></dt><dd>Module sources (repeatable); may consist of supported files and/or directories to recursively search for such files.  Each file will be wrapped within the appropriate markup and bundled into the &lt;head&gt; element of the compiled HTML.  Supported files: <code>.css</code>, <code>.js</code>, <code>.mjs</code>, <code>.otf</code>, <code>.ttf</code>, <code>.woff</code>, <code>.woff2</code>.</dd>
 <dt><kbd>--no-trim</kbd></dt><dd>
 	<p>Do not trim whitespace surrounding passages—i.e., whitespace preceding and trailing the actual text of the passage.  By default, such whitespace is removed when processing passages.</p>
 	<p role="note"><b>Note:</b> It is recommended that you do not disable passage trimming.</p>
@@ -86,7 +86,9 @@ The following extensions are supported:
 <dt><code>.tw</code>, <code>.twee</code></dt>
 <dd>
 	<p>Twee notation source files to process for passages.</p>
-	<p role="note"><b>Note:</b> If any of these files are in the unofficial Twee2 notation, you must manually enable the Twee2 compatibility mode via its command line option (<kbd>--twee2-compat</kbd>).</p>
+	<p role="note"><b>Note:</b>
+	If any of these files are in the unofficial Twee2 notation, you must manually enable the Twee2 compatibility mode via its command line option (<kbd>--twee2-compat</kbd>).
+	</p>
 </dd>
 <dt><code>.tw2</code>, <code>.twee2</code></dt>
 <dd>Unofficial Twee2 notation source files to process for passages.  Twee2 compatibility mode is automatically enabled for files with these extensions.</dd>
@@ -96,6 +98,13 @@ The following extensions are supported:
 <dd>CSS source files to bundle.</dd>
 <dt><code>.js</code></dt>
 <dd>JavaScript source files to bundle.</dd>
+<dt><code>.mjs</code></dt>
+<dd>
+	<p>JavaScript module (ESM) source files to bundle.</p>
+	<p role="note"><b>Note:</b>
+	May only be used with the module option (<kbd>-m SRC</kbd>, <kbd>--module=SRC</kbd>).
+	</p>
+</dd>
 <dt><code>.otf</code>, <code>.ttf</code>, <code>.woff</code>, <code>.woff2</code></dt>
 <dd>Font files to bundle, as <code>@font-face</code> style rules.  The generated name of the font family will be the font's base filename sans its extension—e.g., the family name for <code>chinacat.tff</code> will be <code>chinacat</code>.</dd>
 <dt><code>.gif</code>, <code>.jpeg</code>, <code>.jpg</code>, <code>.png</code>, <code>.svg</code>, <code>.tif</code>, <code>.tiff</code>, <code>.webp</code></dt>

filesystem.go

@@ -244,7 +244,7 @@ func knownFileType(filename string) bool {
 		"tw2", "twee2",
 		"htm", "html",
 		"css",
-		"js",
+		"js", "mjs",
 		"otf", "ttf", "woff", "woff2",
 		"gif", "jpeg", "jpg", "png", "svg", "tif", "tiff", "webp",
 		"aac", "flac", "m4a", "mp3", "oga", "ogg", "opus", "wav", "wave", "weba",

module.go

@@ -1,5 +1,5 @@
 /*
-	Copyright © 2014–2021 Thomas Michael Edwards. All rights reserved.
+	Copyright © 2014–2023 Thomas Michael Edwards. All rights reserved.
 	Use of this source code is governed by a Simplified BSD License which
 	can be found in the LICENSE file.
 */
@@ -33,9 +33,11 @@ func loadModules(filenames []string, encoding string) []byte {
 		switch normalizedFileExt(filename) {
 		// NOTE: The case values here should match those in `filesystem.go:knownFileType()`.
 		case "css":
-			source, err = loadModuleTagged("style", filename, encoding)
+			source, err = loadModuleByType("text/css", filename, encoding)
 		case "js":
-			source, err = loadModuleTagged("script", filename, encoding)
+			source, err = loadModuleByType("text/javascript", filename, encoding)
+		case "mjs":
+			source, err = loadModuleByType("module", filename, encoding)
 		case "otf", "ttf", "woff", "woff2":
 			source, err = loadModuleFont(filename)
 		default:
@@ -55,7 +57,7 @@ func loadModules(filenames []string, encoding string) []byte {
 	return bytes.Join(headTags, []byte("\n"))
 }
 
-func loadModuleTagged(tag, filename, encoding string) ([]byte, error) {
+func loadModuleByType(typeValue, filename, encoding string) ([]byte, error) {
 	source, err := fileReadAllWithEncoding(filename, encoding)
 	if err != nil {
 		return nil, err
@@ -65,24 +67,25 @@ func loadModuleTagged(tag, filename, encoding string) ([]byte, error) {
 		return source, nil
 	}
 
+	var tag string
+	switch typeValue {
+	case "module", "text/javascript":
+		tag = "script"
+	case "text/css":
+		tag = "style"
+	}
+
 	var (
 		idSlug = tag + "-module-" + slugify(strings.Split(filepath.Base(filename), ".")[0])
-		mimeType string
 		b      bytes.Buffer
 	)
-	switch tag {
-	case "script":
-		mimeType = "text/javascript"
-	case "style":
-		mimeType = "text/css"
-	}
 
 	if _, err := fmt.Fprintf(
 		&b,
 		`<%s id=%q type=%q>%s</%[1]s>`,
 		tag,
 		idSlug,
-		mimeType,
+		typeValue,
 		source,
 	); err != nil {
 		return nil, err

storyload.go

@@ -52,6 +52,8 @@ func (s *story) load(filenames []string, c *config) {
 			if err := s.loadTagged("script", filename, c.encoding); err != nil {
 				log.Fatalf("error: load %s: %s", filename, err.Error())
 			}
+		case "mjs":
+			log.Fatalf("error: load %s: ESM files must be loaded via the module option", filename)
 		case "otf", "ttf", "woff", "woff2":
 			if err := s.loadFont(filename); err != nil {
 				log.Fatalf("error: load %s: %s", filename, err.Error())