In the task 圆圈动画 an animated growing circle is shown.

Now let’s say we need not just a circle, but to show a message inside it. The message should appear after the animation is complete (the circle is fully grown), otherwise it would look ugly.

In the solution of the task, the function showCircle(cx, cy, radius) draws the circle, but gives no way to track when it’s ready.

Add a callback argument: showCircle(cx, cy, radius, callback) to be called when the animation is complete. The callback should receive the circle <div> as an argument.

Here’s the example:

showCircle(150, 150, 100, div => {
  div.classList.add('message-ball');
  div.append("Hello, world!");
});

Demo:

Take the solution of the task 圆圈动画 as the base.