wip Stack queue event

src/Stack.ts

@@ -1,7 +1,7 @@
 import {EmittenCommon} from 'emitten';
 
 import {getErrorMessage, fetchAudioBuffer, scratchBuffer} from './helpers';
-import {clamp, msToSec, secToMs} from './utilities';
+import {arrayShallowEquals, clamp, msToSec, secToMs} from './utilities';
 import {tokens} from './tokens';
 
 import type {
@@ -211,8 +211,16 @@ export class Stack extends EmittenCommon<StackEventMap> {
   }
 
   #setQueue(value: Sound[]) {
+    const oldKeys = this._keys;
+    const newKeys = value.map(({id}) => id);
+    const identicalKeys = arrayShallowEquals(oldKeys, newKeys);
+
     this.#queue = value;
-    this._keys = value.map(({id}) => id);
+    this._keys = newKeys;
+
+    if (!identicalKeys) {
+      this.emit('queue', newKeys, oldKeys);
+    }
   }
 
   #setState(value: StackState) {

src/types.ts

@@ -51,6 +51,7 @@ export interface StackError {
 // eslint-disable-next-line @typescript-eslint/consistent-type-definitions
 export type StackEventMap = {
   state: (current: StackState) => void;
+  queue: (newKeys: SoundId[], oldKeys: SoundId[]) => void;
   volume: (level: number) => void;
   mute: (muted: boolean) => void;
   error: (message: StackError) => void;