add ball with click but remove oldest dot when limit reached

src/app/components/dot-background/dot-background.ts

@@ -25,6 +25,9 @@ export class DotBackground implements OnDestroy {
   private lastHeight = 0;
   private readonly RESIZE_THRESHOLD = 100; // ignore small height changes (browser chrome)
 
+  private ballSpawnId = 0;
+  private ballSpawnNextColor = 0;
+
   constructor(private ngZone: NgZone) {
     afterNextRender(() => {
       this.init();
@@ -85,29 +88,48 @@ export class DotBackground implements OnDestroy {
   };
 
   private onMouseClick = () => {
-    if (this.dots.length < this.MAX_DOT_COUNT) {
-      this.dots.push({
-        x: this.mouse.x,
-        y: this.mouse.y,
-        vx: (Math.random() - 0.5) * 0.5,
-        vy: (Math.random() - 0.5) * 0.5,
-        radius: Math.random() * 60 + 40,
-        color: this.COLORS[Math.floor(Math.random() * this.COLORS.length)],
-      });
-    }
+    const dot = this.spawnDot();
+    dot.x = this.mouse.x;
+    dot.y = this.mouse.y;
   };
 
+  private spawnDot(): Dot {
+    const dotId = this.ballSpawnId++;
+    let dot;
+    if (this.ballSpawnId < this.MAX_DOT_COUNT) {
+      dot = {
+        x: 0,
+        y: 0,
+        vx: 0,
+        vy: 0,
+        radius: 1,
+        color: "#000000",
+      };
+
+      this.dots.push(dot);
+    } else {
+      dot = this.dots[dotId % this.MAX_DOT_COUNT];
+    }
+
+    this.populateDot(dot);
+
+    return dot;
+  }
+
+  private populateDot(dot: Dot) {
+    const {width, height} = this.canvasRef.nativeElement;
+
+    dot.x = Math.random() * width;
+    dot.y = Math.random() * height;
+    dot.vx = (Math.random() - 0.5) * 0.5;
+    dot.vy = (Math.random() - 0.5) * 0.5;
+    dot.radius = Math.random() * 60 + 40;
+    dot.color = this.COLORS[this.ballSpawnNextColor++ % this.COLORS.length];
+  }
+
   private initDots() {
-    const { width, height } = this.canvasRef.nativeElement;
     for (let i = 0; i < this.INIT_DOT_COUNT; i++) {
-      this.dots.push({
-        x: Math.random() * width,
-        y: Math.random() * height,
-        vx: (Math.random() - 0.5) * 0.5,
-        vy: (Math.random() - 0.5) * 0.5,
-        radius: Math.random() * 60 + 40,
-        color: this.COLORS[i % this.COLORS.length],
-      });
+      this.spawnDot();
     }
   }