How can I simulate shrink and stretch a rope - Swift - ios

Question

How can I simulate shrink and stretch a rope, I want to joint two sprite nodes and when the getting closer the rope should be stretched and shrunk once they go to the original position, I used a lot of way using Limit and Spring joints but I really don't know how to animate the rope to accomplish the shrink and stretch.
Attempt 1
override func didMove(to view: SKView) {
self.physicsWorld.contactDelegate = self
self.addAnchor()
self.addRope()
self.addCharacter()
let jointOneFixed = SKPhysicsJointFixed.joint(withBodyA: anchor.physicsBody!, bodyB: rope.physicsBody!, anchor: anchor.position)
self.physicsWorld.add(jointOneFixed)
let jointTwoFixed = SKPhysicsJointFixed.joint(withBodyA: rope.physicsBody!, bodyB: currentCharacter.physicsBody!, anchor: CGPoint(x: rope.frame.midX, y: rope.frame.minY))
self.physicsWorld.add(jointTwoFixed)
limitJoint = SKPhysicsJointLimit.joint(withBodyA: anchor.physicsBody!, bodyB: currentCharacter.physicsBody!, anchorA: anchor.position, anchorB: currentCharacter.position)
//limitJoint.maxLength = self.size.height - 1000
self.physicsWorld.add(limitJoint)
}
func addAnchor(){
anchor.position = CGPoint(x: self.size.width / 2, y: self.size.height + 1)
anchor.anchorPoint = CGPoint(x: 0.5, y: 0.5)
anchor.setScale(1)
anchor.zPosition = 2
anchor.name = "anchor"
anchor.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: anchor.size.width, height: anchor.size.height))
anchor.physicsBody?.isDynamic = false
anchor.physicsBody?.affectedByGravity = false
anchor.physicsBody?.allowsRotation = true
self.addChild(anchor)
}
func addRope() {
rope.position = CGPoint(x: anchor.position.x, y: anchor.position.y - 175)
rope.setScale(0.65)
rope.zPosition = 1
rope.name = "rope"
rope.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: rope.size.width, height: rope.size.height))
rope.physicsBody?.affectedByGravity = false;
rope.physicsBody?.mass = 0.5;
rope.physicsBody?.allowsRotation = true
self.addChild(rope)
}
func addCharacter() {
let characterName: String = UserDefaults.standard.string(forKey: "current_character")!
currentCharacter = SKSpriteNode(imageNamed: characterName);
currentCharacter.position = CGPoint(x: self.size.width / 2, y: self.size.height - 400)
currentCharacter.anchorPoint = CGPoint(x: 0.5, y: 0.5)
currentCharacter.setScale(0.50)
currentCharacter.zPosition = 2
currentCharacter.name = "character"
currentCharacter.physicsBody = SKPhysicsBody(circleOfRadius: max(currentCharacter.size.width / 2, currentCharacter.size.height / 2))
currentCharacter.physicsBody?.affectedByGravity = false
currentCharacter.physicsBody?.isDynamic = true
currentCharacter.physicsBody?.allowsRotation = true
self.addChild(currentCharacter)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
let moveDown = SKAction.moveBy(x: 0, y: -100, duration:0.1)
currentCharacter.run(moveDown)
}
Attempt 2
Is almost the same except instead of create a Limit joint I created a Spring joint
override func didMove(to view: SKView) {
self.physicsWorld.contactDelegate = self
self.addAnchor()
self.addRope()
self.addCharacter()
let jointOneFixed = SKPhysicsJointFixed.joint(withBodyA: anchor.physicsBody!, bodyB: rope.physicsBody!, anchor: anchor.position)
self.physicsWorld.add(jointOneFixed)
let jointTwoFixed = SKPhysicsJointFixed.joint(withBodyA: rope.physicsBody!, bodyB: currentCharacter.physicsBody!, anchor: CGPoint(x: rope.frame.midX, y: rope.frame.minY))
self.physicsWorld.add(jointTwoFixed)
let springJoint = SKPhysicsJointSpring.joint(withBodyA: anchor.physicsBody!, bodyB: currentCharacter.physicsBody!, anchorA: anchor.position, anchorB: currentCharacter.position)
//springJoint.frequency = 1.0
//springJoint.damping = 0
self.physicsWorld.add(springJoint)
}