Migrate features module to TypeScript

src/annotator/features.js → src/annotator/features.ts

 import { TinyEmitter } from 'tiny-emitter';
 
 import { warnOnce } from '../shared/warn-once';
-
-/**
- * @typedef {import('../types/annotator').FeatureFlags} IFeatureFlags
- */
+import type { FeatureFlags as IFeatureFlags } from '../types/annotator';
 
 /**
  * List of feature flags that annotator code tests for.
- *
- * @type {string[]}
  */
 const annotatorFlags = ['html_side_by_side', 'styled_highlight_clusters'];
 
 /**
  * An observable container of feature flags.
- *
- * @implements {IFeatureFlags}
  */
-export class FeatureFlags extends TinyEmitter {
+export class FeatureFlags extends TinyEmitter implements IFeatureFlags {
+  /** Map of flag name to enabled state. */
+  private _flags: Map<string, boolean>;
+  private _knownFlags: string[];
+
   /**
-   * @param {string[]} knownFlags - Test seam. This is a list of known flags
-   *   used to catch mistakes where code checks for an obsolete feature flag.
+   * @param knownFlags - Test seam. This is a list of known flags used to catch
+   *        mistakes where code checks for an obsolete feature flag.
    */
-  constructor(knownFlags = annotatorFlags) {
+  constructor(knownFlags: string[] = annotatorFlags) {
     super();
 
-    /**
-     * Map of flag name to enabled state.
-     *
-     * @type {Map<string, boolean>}
-     */
-    this._flags = new Map();
+    this._flags = new Map<string, boolean>();
     this._knownFlags = knownFlags;
   }
 
   /**
    * Update the stored flags and notify observers via a "flagsChanged" event.
-   *
-   * @param {Record<string, boolean>} flags
    */
-  update(flags) {
+  update(flags: Record<string, boolean>) {
     this._flags.clear();
-    for (let [flag, on] of Object.entries(flags)) {
+    for (const [flag, on] of Object.entries(flags)) {
       this._flags.set(flag, on);
     }
     this.emit('flagsChanged');
@@ -54,11 +44,8 @@ export class FeatureFlags extends TinyEmitter {
    * This will return false if the feature flags have not yet been received from
    * the backend. Code that uses a feature flag should handle subsequent changes
    * to the flag's state by listening for the "flagsChanged" event.
-   *
-   * @param {string} flag
-   * @return {boolean}
    */
-  flagEnabled(flag) {
+  flagEnabled(flag: string): boolean {
     if (!this._knownFlags.includes(flag)) {
       warnOnce('Looked up unknown feature', flag);
       return false;
@@ -72,7 +59,7 @@ export class FeatureFlags extends TinyEmitter {
    * To test whether an individual flag is enabled, use {@link flagEnabled}
    * instead.
    */
-  allFlags() {
+  allFlags(): Record<string, boolean> {
     return Object.fromEntries(this._flags);
   }
 }