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diff --git a/ext/mixed/js/hotkey-handler.js b/ext/mixed/js/hotkey-handler.js
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+++ b/ext/mixed/js/hotkey-handler.js
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+/*
+ * Copyright (C) 2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* global
+ * DocumentUtil
+ */
+
+/**
+ * Class which handles hotkey events and actions.
+ */
+class HotkeyHandler extends EventDispatcher {
+    /**
+     * Creates a new instance of the class.
+     * @param scope The scope required for hotkey definitions.
+     */
+    constructor(scope) {
+        super();
+        this._scope = scope;
+        this._hotkeys = new Map();
+        this._actions = new Map();
+        this._eventListeners = new EventListenerCollection();
+    }
+
+    /**
+     * Gets the scope required for the hotkey definitions.
+     */
+    get scope() {
+        return this._scope;
+    }
+
+    /**
+     * Sets the scope required for the hotkey definitions.
+     */
+    set scope(value) {
+        this._scope = value;
+    }
+
+    /**
+     * Begins listening to key press events in order to detect hotkeys.
+     */
+    prepare() {
+        this._eventListeners.addEventListener(document, 'keydown', this._onKeyDown.bind(this), false);
+    }
+
+    /**
+     * Stops listening to key press events.
+     */
+    cleanup() {
+        this._eventListeners.removeAllEventListeners();
+    }
+
+    /**
+     * Registers a set of actions that this hotkey handler supports.
+     * @param actions An array of `[name, handler]` entries, where `name` is a string and `handler` is a function.
+     */
+    registerActions(actions) {
+        for (const [name, handler] of actions) {
+            this._actions.set(name, handler);
+        }
+    }
+
+    /**
+     * Registers a set of hotkeys
+     * @param hotkeys An array of hotkey definitions of the format `{action, key, modifiers, scopes, enabled}`.
+     * * `action` - a string indicating which action to perform.
+     * * `key` - a keyboard key code indicating which key needs to be pressed.
+     * * `modifiers` - an array of keyboard modifiers which also need to be pressed. Supports: `'alt', 'ctrl', 'shift', 'meta'`.
+     * * `scopes` - an array of scopes for which the hotkey is valid. If this array does not contain `this.scope`, the hotkey will not be registered.
+     * * `enabled` - a boolean indicating whether the hotkey is currently enabled.
+     */
+    registerHotkeys(hotkeys) {
+        for (const {action, key, modifiers, scopes, enabled} of hotkeys) {
+            if (
+                enabled &&
+                action !== '' &&
+                scopes.includes(this._scope)
+            ) {
+                this._registerHotkey(key, modifiers, action);
+            }
+        }
+    }
+
+    /**
+     * Removes all registered hotkeys.
+     */
+    clearHotkeys() {
+        this._hotkeys.clear();
+    }
+
+    // Private
+
+    _onKeyDown(e) {
+        const key = e.code;
+        const handlers = this._hotkeys.get(key);
+        if (typeof handlers !== 'undefined') {
+            const eventModifiers = DocumentUtil.getActiveModifiers(e);
+            for (const {modifiers, action} of handlers) {
+                if (!this._areSame(modifiers, eventModifiers)) { continue; }
+
+                const actionHandler = this._actions.get(action);
+                if (typeof actionHandler === 'undefined') { continue; }
+
+                const result = actionHandler(e);
+                if (result !== false) {
+                    e.preventDefault();
+                    return true;
+                }
+            }
+        }
+        this.trigger('keydownNonHotkey', e);
+        return false;
+    }
+
+    _registerHotkey(key, modifiers, action) {
+        let handlers = this._hotkeys.get(key);
+        if (typeof handlers === 'undefined') {
+            handlers = [];
+            this._hotkeys.set(key, handlers);
+        }
+        handlers.push({modifiers: new Set(modifiers), action});
+    }
+
+    _areSame(set, array) {
+        if (set.size !== array.length) { return false; }
+        for (const value of array) {
+            if (!set.has(value)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}