Add JSDoc type annotations to project (rebased)

1 files changed, 258 insertions, 89 deletions

diff --git a/ext/js/templates/sandbox/anki-template-renderer.js b/ext/js/templates/sandbox/anki-template-renderer.js
index 10f69745..ce8e3200 100644
--- a/ext/js/templates/sandbox/anki-template-renderer.js
+++ b/ext/js/templates/sandbox/anki-template-renderer.js
@@ -36,17 +36,29 @@ export class AnkiTemplateRenderer {
      * Creates a new instance of the class.
      */
     constructor() {
+        /** @type {CssStyleApplier} */
         this._structuredContentStyleApplier = new CssStyleApplier('/data/structured-content-style.json');
+        /** @type {CssStyleApplier} */
         this._pronunciationStyleApplier = new CssStyleApplier('/data/pronunciation-style.json');
+        /** @type {RegExp} */
         this._structuredContentDatasetKeyIgnorePattern = /^sc([^a-z]|$)/;
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = new JapaneseUtil(null);
+        /** @type {TemplateRenderer} */
         this._templateRenderer = new TemplateRenderer();
+        /** @type {AnkiNoteDataCreator} */
         this._ankiNoteDataCreator = new AnkiNoteDataCreator(this._japaneseUtil);
+        /** @type {TemplateRendererMediaProvider} */
         this._mediaProvider = new TemplateRendererMediaProvider();
+        /** @type {PronunciationGenerator} */
         this._pronunciationGenerator = new PronunciationGenerator(this._japaneseUtil);
+        /** @type {?(Map<string, unknown>[])} */
         this._stateStack = null;
+        /** @type {?import('anki-note-builder').Requirement[]} */
         this._requirements = null;
-        this._cleanupCallbacks = null;
+        /** @type {(() => void)[]} */
+        this._cleanupCallbacks = [];
+        /** @type {?HTMLElement} */
         this._temporaryElement = null;
     }
 
@@ -93,7 +105,7 @@ export class AnkiTemplateRenderer {
         ]);
         this._templateRenderer.registerDataType('ankiNote', {
             modifier: ({marker, commonData}) => this._ankiNoteDataCreator.create(marker, commonData),
-            composeData: (marker, commonData) => ({marker, commonData})
+            composeData: ({marker}, commonData) => ({marker, commonData})
         });
         this._templateRenderer.setRenderCallbacks(
             this._onRenderSetup.bind(this),
@@ -107,40 +119,56 @@ export class AnkiTemplateRenderer {
 
     // Private
 
+    /**
+     * @returns {{requirements: import('anki-note-builder').Requirement[]}}
+     */
     _onRenderSetup() {
+        /** @type {import('anki-note-builder').Requirement[]} */
         const requirements = [];
         this._stateStack = [new Map()];
         this._requirements = requirements;
         this._mediaProvider.requirements = requirements;
-        this._cleanupCallbacks = [];
         return {requirements};
     }
 
+    /**
+     * @returns {void}
+     */
     _onRenderCleanup() {
         for (const callback of this._cleanupCallbacks) { callback(); }
         this._stateStack = null;
         this._requirements = null;
         this._mediaProvider.requirements = null;
-        this._cleanupCallbacks = null;
+        this._cleanupCallbacks.length = 0;
     }
 
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _escape(text) {
         return Handlebars.Utils.escapeExpression(text);
     }
 
+    /**
+     *
+     * @param text
+     */
     _safeString(text) {
         return new Handlebars.SafeString(text);
     }
 
     // Template helpers
 
-    _dumpObject(context, object) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _dumpObject(object) {
         const dump = JSON.stringify(object, null, 4);
         return this._escape(dump);
     }
 
-    _furigana(context, ...args) {
-        const {expression, reading} = this._getFuriganaExpressionAndReading(context, ...args);
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _furigana(args, context, options) {
+        const {expression, reading} = this._getFuriganaExpressionAndReading(args, context, options);
         const segs = this._japaneseUtil.distributeFurigana(expression, reading);
 
         let result = '';
@@ -157,8 +185,9 @@ export class AnkiTemplateRenderer {
         return this._safeString(result);
     }
 
-    _furiganaPlain(context, ...args) {
-        const {expression, reading} = this._getFuriganaExpressionAndReading(context, ...args);
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _furiganaPlain(args, context, options) {
+        const {expression, reading} = this._getFuriganaExpressionAndReading(args, context, options);
         const segs = this._japaneseUtil.distributeFurigana(expression, reading);
 
         let result = '';
@@ -174,43 +203,56 @@ export class AnkiTemplateRenderer {
         return result;
     }
 
-    _getFuriganaExpressionAndReading(context, ...args) {
-        if (args.length >= 3) {
-            return {expression: args[0], reading: args[1]};
-        } else if (args.length === 2) {
-            const {expression, reading} = args[0];
-            return {expression, reading};
+    /**
+     * @type {import('template-renderer').HelperFunction<{expression: string, reading: string}>}
+     */
+    _getFuriganaExpressionAndReading(args) {
+        let expression;
+        let reading;
+        if (args.length >= 2) {
+            [expression, reading] = /** @type {[expression?: string, reading?: string]} */ (args);
         } else {
-            return void 0;
+            ({expression, reading} = /** @type {import('core').SerializableObject} */ (args[0]));
         }
+        return {
+            expression: typeof expression === 'string' ? expression : '',
+            reading: typeof reading === 'string' ? reading : ''
+        };
     }
 
+    /**
+     *
+     * @param string
+     */
     _stringToMultiLineHtml(string) {
         return string.split('\n').join('<br>');
     }
 
-    _multiLine(context, options) {
-        return this._stringToMultiLineHtml(options.fn(context));
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _multiLine(_args, context, options) {
+        return this._stringToMultiLineHtml(this._asString(options.fn(context)));
     }
 
-    _regexReplace(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _regexReplace(args, context, options) {
         // Usage:
         // {{#regexReplace regex string [flags] [content]...}}content{{/regexReplace}}
         // regex: regular expression string
         // string: string to replace
         // flags: optional flags for regular expression
         //   e.g. "i" for case-insensitive, "g" for replace all
-        const argCount = args.length - 1;
-        const options = args[argCount];
-        let value = typeof options.fn === 'function' ? options.fn(context) : '';
+        const argCount = args.length;
+        let value = this._asString(options.fn(context));
         if (argCount > 3) {
             value = `${args.slice(3, -1).join('')}${value}`;
         }
         if (argCount > 1) {
             try {
-                const flags = argCount > 2 ? args[2] : 'g';
-                const regex = new RegExp(args[0], flags);
-                value = value.replace(regex, args[1]);
+                const [pattern, replacement, flags] = args;
+                if (typeof pattern !== 'string') { throw new Error('Invalid pattern'); }
+                if (typeof replacement !== 'string') { throw new Error('Invalid replacement'); }
+                const regex = new RegExp(pattern, typeof flags === 'string' ? flags : 'g');
+                value = value.replace(regex, replacement);
             } catch (e) {
                 return `${e}`;
             }
@@ -218,24 +260,26 @@ export class AnkiTemplateRenderer {
         return value;
     }
 
-    _regexMatch(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _regexMatch(args, context, options) {
         // Usage:
         // {{#regexMatch regex [flags] [content]...}}content{{/regexMatch}}
         // regex: regular expression string
         // flags: optional flags for regular expression
         //   e.g. "i" for case-insensitive, "g" for match all
-        const argCount = args.length - 1;
-        const options = args[argCount];
-        let value = typeof options.fn === 'function' ? options.fn(context) : '';
+        const argCount = args.length;
+        let value = this._asString(options.fn(context));
         if (argCount > 2) {
             value = `${args.slice(2, -1).join('')}${value}`;
         }
         if (argCount > 0) {
             try {
-                const flags = argCount > 1 ? args[1] : '';
-                const regex = new RegExp(args[0], flags);
+                const [pattern, flags] = args;
+                if (typeof pattern !== 'string') { throw new Error('Invalid pattern'); }
+                const regex = new RegExp(pattern, typeof flags === 'string' ? flags : '');
+                /** @type {string[]} */
                 const parts = [];
-                value.replace(regex, (g0) => parts.push(g0));
+                value.replace(regex, (g0) => { parts.push(g0); return g0; });
                 value = parts.join('');
             } catch (e) {
                 return `${e}`;
@@ -244,11 +288,18 @@ export class AnkiTemplateRenderer {
         return value;
     }
 
-    _mergeTags(context, object, isGroupMode, isMergeMode) {
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _mergeTags(args) {
+        const [object, isGroupMode, isMergeMode] = /** @type {[object: import('anki-templates').TermDictionaryEntry, isGroupMode: boolean, isMergeMode: boolean]} */ (args);
         const tagSources = [];
         if (isGroupMode || isMergeMode) {
-            for (const definition of object.definitions) {
-                tagSources.push(definition.definitionTags);
+            const {definitions} = object;
+            if (Array.isArray(definitions)) {
+                for (const definition of definitions) {
+                    tagSources.push(definition.definitionTags);
+                }
             }
         } else {
             tagSources.push(object.definitionTags);
@@ -265,7 +316,9 @@ export class AnkiTemplateRenderer {
         return [...tags].join(', ');
     }
 
-    _eachUpTo(context, iterable, maxCount, options) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _eachUpTo(args, context, options) {
+        const [iterable, maxCount] = /** @type {[iterable: Iterable<unknown>, maxCount: number]} */ (args);
         if (iterable) {
             const results = [];
             let any = false;
@@ -279,14 +332,15 @@ export class AnkiTemplateRenderer {
                 return results.join('');
             }
         }
-        return options.inverse(context);
+        return this._asString(options.inverse(context));
     }
 
-    _spread(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<unknown[]>} */
+    _spread(args) {
         const result = [];
-        for (let i = 0, ii = args.length - 1; i < ii; ++i) {
+        for (const array of /** @type {Iterable<unknown>[]} */ (args)) {
             try {
-                result.push(...args[i]);
+                result.push(...array);
             } catch (e) {
                 // NOP
             }
@@ -294,15 +348,22 @@ export class AnkiTemplateRenderer {
         return result;
     }
 
-    _op(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _op(args) {
+        const [operator] = /** @type {[operator: string, operand1: import('core').SafeAny, operand2?: import('core').SafeAny, operand3?: import('core').SafeAny]} */ (args);
         switch (args.length) {
-            case 3: return this._evaluateUnaryExpression(args[0], args[1]);
-            case 4: return this._evaluateBinaryExpression(args[0], args[1], args[2]);
-            case 5: return this._evaluateTernaryExpression(args[0], args[1], args[2], args[3]);
+            case 2: return this._evaluateUnaryExpression(operator, args[1]);
+            case 3: return this._evaluateBinaryExpression(operator, args[1], args[2]);
+            case 4: return this._evaluateTernaryExpression(operator, args[1], args[2], args[3]);
             default: return void 0;
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @returns {unknown}
+     */
     _evaluateUnaryExpression(operator, operand1) {
         switch (operator) {
             case '+': return +operand1;
@@ -313,6 +374,12 @@ export class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @param {import('core').SafeAny} operand2
+     * @returns {unknown}
+     */
     _evaluateBinaryExpression(operator, operand1, operand2) {
         switch (operator) {
             case '+': return operand1 + operand2;
@@ -341,6 +408,13 @@ export class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @param {import('core').SafeAny} operand2
+     * @param {import('core').SafeAny} operand3
+     * @returns {unknown}
+     */
     _evaluateTernaryExpression(operator, operand1, operand2, operand3) {
         switch (operator) {
             case '?:': return operand1 ? operand2 : operand3;
@@ -348,8 +422,11 @@ export class AnkiTemplateRenderer {
         }
     }
 
-    _get(context, key) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _get(args) {
+        const [key] = /** @type {[key: string]} */ (args);
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         for (let i = stateStack.length; --i >= 0;) {
             const map = stateStack[i];
             if (map.has(key)) {
@@ -359,19 +436,21 @@ export class AnkiTemplateRenderer {
         return void 0;
     }
 
-    _set(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _set(args, context, options) {
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         switch (args.length) {
-            case 2:
+            case 1:
                 {
-                    const [key, options] = args;
+                    const [key] = /** @type {[key: string]} */ (args);
                     const value = options.fn(context);
                     stateStack[stateStack.length - 1].set(key, value);
                 }
                 break;
-            case 3:
+            case 2:
                 {
-                    const [key, value] = args;
+                    const [key, value] = /** @type {[key: string, value: unknown]} */ (args);
                     stateStack[stateStack.length - 1].set(key, value);
                 }
                 break;
@@ -379,8 +458,10 @@ export class AnkiTemplateRenderer {
         return '';
     }
 
-    _scope(context, options) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _scope(_args, context, options) {
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         try {
             stateStack.push(new Map());
             return options.fn(context);
@@ -391,14 +472,25 @@ export class AnkiTemplateRenderer {
         }
     }
 
-    _property(context, ...args) {
-        const ii = args.length - 1;
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _property(args) {
+        const ii = args.length;
         if (ii <= 0) { return void 0; }
 
         try {
             let value = args[0];
             for (let i = 1; i < ii; ++i) {
-                value = value[args[i]];
+                if (typeof value !== 'object' || value === null) { throw new Error('Invalid object'); }
+                const key = args[i];
+                switch (typeof key) {
+                    case 'number':
+                    case 'string':
+                    case 'symbol':
+                        break;
+                    default:
+                        throw new Error('Invalid key');
+                }
+                value = /** @type {import('core').UnknownObject} */ (value)[key];
             }
             return value;
         } catch (e) {
@@ -406,38 +498,51 @@ export class AnkiTemplateRenderer {
         }
     }
 
-    _noop(context, options) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _noop(_args, context, options) {
         return options.fn(context);
     }
 
-    _isMoraPitchHigh(context, index, position) {
+    /** @type {import('template-renderer').HelperFunction<boolean>} */
+    _isMoraPitchHigh(args) {
+        const [index, position] = /** @type {[index: number, position: number]} */ (args);
         return this._japaneseUtil.isMoraPitchHigh(index, position);
     }
 
-    _getKanaMorae(context, text) {
+    /** @type {import('template-renderer').HelperFunction<string[]>} */
+    _getKanaMorae(args) {
+        const [text] = /** @type {[text: string]} */ (args);
         return this._japaneseUtil.getKanaMorae(`${text}`);
     }
 
-    _getTypeof(context, ...args) {
-        const ii = args.length - 1;
-        const value = (ii > 0 ? args[0] : args[ii].fn(context));
+    /** @type {import('template-renderer').HelperFunction<import('core').TypeofResult>} */
+    _getTypeof(args, context, options) {
+        const ii = args.length;
+        const value = (ii > 0 ? args[0] : options.fn(context));
         return typeof value;
     }
 
-    _join(context, ...args) {
-        return args.length > 1 ? args.slice(1, args.length - 1).flat().join(args[0]) : '';
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _join(args) {
+        return args.length > 0 ? args.slice(1, args.length).flat().join(/** @type {string} */ (args[0])) : '';
     }
 
-    _concat(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _concat(args) {
         let result = '';
-        for (let i = 0, ii = args.length - 1; i < ii; ++i) {
+        for (let i = 0, ii = args.length; i < ii; ++i) {
             result += args[i];
         }
         return result;
     }
 
-    _pitchCategories(context, data) {
-        const {pronunciations, headwords} = data.dictionaryEntry;
+    /** @type {import('template-renderer').HelperFunction<string[]>} */
+    _pitchCategories(args) {
+        const [data] = /** @type {[data: import('anki-templates').NoteData]} */ (args);
+        const {dictionaryEntry} = data;
+        if (dictionaryEntry.type !== 'term') { return []; }
+        const {pronunciations, headwords} = dictionaryEntry;
+        /** @type {Set<string>} */
         const categories = new Set();
         for (const {headwordIndex, pitches} of pronunciations) {
             const {reading, wordClasses} = headwords[headwordIndex];
@@ -452,6 +557,9 @@ export class AnkiTemplateRenderer {
         return [...categories];
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     _getTemporaryElement() {
         let element = this._temporaryElement;
         if (element === null) {
@@ -461,14 +569,28 @@ export class AnkiTemplateRenderer {
         return element;
     }
 
+    /**
+     * @param {Element} node
+     * @returns {string}
+     */
     _getStructuredContentHtml(node) {
         return this._getHtml(node, this._structuredContentStyleApplier, this._structuredContentDatasetKeyIgnorePattern);
     }
 
+    /**
+     * @param {Element} node
+     * @returns {string}
+     */
     _getPronunciationHtml(node) {
         return this._getHtml(node, this._pronunciationStyleApplier, null);
     }
 
+    /**
+     * @param {Element} node
+     * @param {CssStyleApplier} styleApplier
+     * @param {?RegExp} datasetKeyIgnorePattern
+     * @returns {string}
+     */
     _getHtml(node, styleApplier, datasetKeyIgnorePattern) {
         const container = this._getTemporaryElement();
         container.appendChild(node);
@@ -478,20 +600,27 @@ export class AnkiTemplateRenderer {
         return this._safeString(result);
     }
 
+    /**
+     * @param {Element} root
+     * @param {CssStyleApplier} styleApplier
+     * @param {?RegExp} datasetKeyIgnorePattern
+     */
     _normalizeHtml(root, styleApplier, datasetKeyIgnorePattern) {
         const {ELEMENT_NODE, TEXT_NODE} = Node;
         const treeWalker = document.createTreeWalker(root, NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_TEXT);
+        /** @type {HTMLElement[]} */
         const elements = [];
+        /** @type {Text[]} */
         const textNodes = [];
         while (true) {
             const node = treeWalker.nextNode();
             if (node === null) { break; }
             switch (node.nodeType) {
                 case ELEMENT_NODE:
-                    elements.push(node);
+                    elements.push(/** @type {HTMLElement} */ (node));
                     break;
                 case TEXT_NODE:
-                    textNodes.push(node);
+                    textNodes.push(/** @type {Text} */ (node));
                     break;
             }
         }
@@ -508,8 +637,11 @@ export class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {Text} textNode
+     */
     _replaceNewlines(textNode) {
-        const parts = textNode.nodeValue.split('\n');
+        const parts = /** @type {string} */ (textNode.nodeValue).split('\n');
         if (parts.length <= 1) { return; }
         const {parentNode} = textNode;
         if (parentNode === null) { return; }
@@ -521,6 +653,10 @@ export class AnkiTemplateRenderer {
         parentNode.replaceChild(fragment, textNode);
     }
 
+    /**
+     * @param {import('anki-templates').NoteData} data
+     * @returns {StructuredContentGenerator}
+     */
     _createStructuredContentGenerator(data) {
         const contentManager = new AnkiTemplateRendererContentManager(this._mediaProvider, data);
         const instance = new StructuredContentGenerator(contentManager, this._japaneseUtil, document);
@@ -528,44 +664,65 @@ export class AnkiTemplateRenderer {
         return instance;
     }
 
-    _formatGlossary(context, dictionary, content, options) {
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _formatGlossary(args, context, options) {
+        const [dictionary] = /** @type {[dictionary: string]} */ (args);
         const data = options.data.root;
+        const content = /** @type {import('dictionary-data').TermGlossary} */ (args[0]);
         if (typeof content === 'string') { return this._stringToMultiLineHtml(this._escape(content)); }
         if (!(typeof content === 'object' && content !== null)) { return ''; }
         switch (content.type) {
             case 'image': return this._formatGlossaryImage(content, dictionary, data);
             case 'structured-content': return this._formatStructuredContent(content, dictionary, data);
+            case 'text': return this._stringToMultiLineHtml(this._escape(content.text));
         }
         return '';
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryImage} content
+     * @param {string} dictionary
+     * @param {import('anki-templates').NoteData} data
+     * @returns {string}
+     */
     _formatGlossaryImage(content, dictionary, data) {
         const structuredContentGenerator = this._createStructuredContentGenerator(data);
         const node = structuredContentGenerator.createDefinitionImage(content, dictionary);
         return this._getStructuredContentHtml(node);
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryStructuredContent} content
+     * @param {string} dictionary
+     * @param {import('anki-templates').NoteData} data
+     * @returns {string}
+     */
     _formatStructuredContent(content, dictionary, data) {
         const structuredContentGenerator = this._createStructuredContentGenerator(data);
         const node = structuredContentGenerator.createStructuredContent(content.content, dictionary);
         return node !== null ? this._getStructuredContentHtml(node) : '';
     }
 
-    _hasMedia(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
-        return this._mediaProvider.hasMedia(options.data.root, args.slice(0, ii), options.hash);
+    /**
+     * @type {import('template-renderer').HelperFunction<boolean>}
+     */
+    _hasMedia(args, _context, options) {
+        return this._mediaProvider.hasMedia(options.data.root, args, options.hash);
     }
 
-    _getMedia(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
-        return this._mediaProvider.getMedia(options.data.root, args.slice(0, ii), options.hash);
+    /**
+     * @type {import('template-renderer').HelperFunction<?string>}
+     */
+    _getMedia(args, _context, options) {
+        return this._mediaProvider.getMedia(options.data.root, args, options.hash);
     }
 
-    _pronunciation(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _pronunciation(_args, _context, options) {
         let {format, reading, downstepPosition, nasalPositions, devoicePositions} = options.hash;
 
         if (typeof reading !== 'string' || reading.length === 0) { return ''; }
@@ -586,18 +743,30 @@ export class AnkiTemplateRenderer {
         }
     }
 
-    _hiragana(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _hiragana(args, context, options) {
+        const ii = args.length;
         const {keepProlongedSoundMarks} = options.hash;
         const value = (ii > 0 ? args[0] : options.fn(context));
-        return this._japaneseUtil.convertKatakanaToHiragana(value, keepProlongedSoundMarks === true);
+        return typeof value === 'string' ? this._japaneseUtil.convertKatakanaToHiragana(value, keepProlongedSoundMarks === true) : '';
     }
 
-    _katakana(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _katakana(args, context, options) {
+        const ii = args.length;
         const value = (ii > 0 ? args[0] : options.fn(context));
-        return this._japaneseUtil.convertHiraganaToKatakana(value);
+        return typeof value === 'string' ? this._japaneseUtil.convertHiraganaToKatakana(value) : '';
+    }
+
+    /**
+     * @param {unknown} value
+     * @returns {string}
+     */
+    _asString(value) {
+        return typeof value === 'string' ? value : `${value}`;
     }
 }