Use tempo stored in stage

src/extensions/scratch3_music/index.js

@@ -43,13 +43,6 @@ class Scratch3MusicBlocks {
          */
         this.runtime = runtime;
 
-        /**
-         * The current tempo in beats per minute. The tempo is a global property of the project,
-         * not a property of each sprite, so it is not stored in the MusicState object.
-         * @type {number}
-         */
-        this.tempo = 60;
-
         /**
          * The number of drum and instrument sounds currently being played simultaneously.
          * @type {number}
@@ -759,7 +752,7 @@ class Scratch3MusicBlocks {
      * @private
      */
     _beatsToSec (beats) {
-        return (60 / this.tempo) * beats;
+        return (60 / this.getTempo()) * beats;
     }
 
     /**
@@ -829,7 +822,7 @@ class Scratch3MusicBlocks {
      */
     changeTempo (args) {
         const change = Cast.toNumber(args.TEMPO);
-        const tempo = change + this.tempo;
+        const tempo = change + this.getTempo();
         this._updateTempo(tempo);
     }
 
@@ -840,7 +833,10 @@ class Scratch3MusicBlocks {
      */
     _updateTempo (tempo) {
         tempo = MathUtil.clamp(tempo, Scratch3MusicBlocks.TEMPO_RANGE.min, Scratch3MusicBlocks.TEMPO_RANGE.max);
-        this.tempo = tempo;
+        const stage = this.runtime.getTargetForStage();
+        if (stage) {
+            stage.tempo = tempo;
+        }
     }
 
     /**
@@ -848,7 +844,11 @@ class Scratch3MusicBlocks {
      * @return {number} - the current tempo, in beats per minute.
      */
     getTempo () {
-        return this.tempo;
+        const stage = this.runtime.getTargetForStage();
+        if (stage) {
+            return stage.tempo;
+        }
+        return 60;
     }
 }