SpriteKit

  func animateNodes(nodes: [SKNode]) {
    for (index, node) in nodes.enumerated() {
      let delayAction = SKAction.wait(forDuration: TimeInterval(index) * 0.2)

      let scaleUpAction = SKAction.scale(to: 1.5, duration: 0.3)
      let scaleDownAction = SKAction.scale(to: 1, duration: 0.3)

      let waitAction = SKAction.wait(forDuration: 2)

      let scaleActionSequence = SKAction.sequence([scaleUpAction, scaleDownAction, waitAction])

      let repeatAction = SKAction.repeatForever(scaleActionSequence)

      let actionSequence = SKAction.sequence([delayAction, repeatAction])

      node.run(actionSequence)
    }
  }

// the same:

  func animateNodes2(nodes: [SKNode]) {
    for (index, node) in nodes.enumerated() {
      node.run(.sequence([
        .wait(forDuration: TimeInterval(index) * 0.2),
        .repeatForever(.sequence([
          .scale(to: 1.5, duration: 0.3),
          .scale(to: 1, duration: 0.3),
          .wait(forDuration: 2),
          ]))
        ]))
    }
  }