Optimize Anki duplicate checks (#1013)

* Move/rename functions

* Prevent overlapping calls to check addable definitions

ext/mixed/js/display.js

@@ -86,6 +86,7 @@ class Display extends EventDispatcher {
         this._ankiNoteBuilder = new AnkiNoteBuilder({
             renderTemplate: this._renderTemplate.bind(this)
         });
+        this._updateAdderButtonsPromise = Promise.resolve();
 
         this.registerActions([
             ['close',            () => { this.onEscape(); }],
@@ -892,32 +893,11 @@ class Display extends EventDispatcher {
             this.autoPlayAudio();
         }
 
-        this._setContentTermsOrKanjiUpdateAdderButtons(token, isTerms, definitions);
+        this._updateAdderButtons(token, isTerms, definitions);
 
         return true;
     }
 
-    async _setContentTermsOrKanjiUpdateAdderButtons(token, isTerms, definitions) {
-        const modes = isTerms ? ['term-kanji', 'term-kana'] : ['kanji'];
-        let states;
-        try {
-            if (this._options.anki.checkForDuplicates) {
-                const noteContext = await this._getNoteContext();
-                states = await this._areDefinitionsAddable(definitions, modes, noteContext);
-            } else {
-                if (!await api.isAnkiConnected()) {
-                    throw new Error('Anki not connected');
-                }
-                states = this._areDefinitionsAddableForcedValue(definitions, modes, true);
-            }
-        } catch (e) {
-            return;
-        }
-        if (this._setContentToken !== token) { return; }
-
-        this._updateAdderButtons(states, modes);
-    }
-
     _setContentExtensionUnloaded() {
         const errorExtensionUnloaded = document.querySelector('#error-extension-unloaded');
 
@@ -976,7 +956,39 @@ class Display extends EventDispatcher {
         this._navigationHeader.dataset.hasNext = `${!!next}`;
     }
 
-    _updateAdderButtons(states, modes) {
+    async _updateAdderButtons(token, isTerms, definitions) {
+        await this._updateAdderButtonsPromise;
+        if (this._setContentToken !== token) { return; }
+
+        const {promise, resolve} = deferPromise();
+        try {
+            this._updateAdderButtonsPromise = promise;
+
+            const modes = isTerms ? ['term-kanji', 'term-kana'] : ['kanji'];
+            let states;
+            try {
+                if (this._options.anki.checkForDuplicates) {
+                    const noteContext = await this._getNoteContext();
+                    states = await this._areDefinitionsAddable(definitions, modes, noteContext);
+                } else {
+                    if (!await api.isAnkiConnected()) {
+                        throw new Error('Anki not connected');
+                    }
+                    states = this._areDefinitionsAddableForcedValue(definitions, modes, true);
+                }
+            } catch (e) {
+                return;
+            }
+
+            if (this._setContentToken !== token) { return; }
+
+            this._updateAdderButtons2(states, modes);
+        } finally {
+            resolve();
+        }
+    }
+
+    _updateAdderButtons2(states, modes) {
         for (let i = 0, ii = states.length; i < ii; ++i) {
             const infos = states[i];
             let noteId = null;