rebound

advance

be uesd in 
loop

class spring

export class Spring {
  static MAX_DELTA_TIME_SEC: number;
  static SOLVER_TIMESTEP_SEC: number;

  listeners: Array<Listener>|null;

  constructor(system: SpringSystem);

  destroy(): void;

  getId(): number;

  getSpringConfig(): SpringConfigDict;
  setSpringConfig(value: SpringConfigDict): Spring;

  getCurrentValue(): number;
  setCurrentValue(currentValue: number, skipSetAtRest?: boolean): Spring;

  getStartValue(): number;

  getCurrentDisplacementDistance(): number;
  getCurrentDisplacementDistanceForState(state: PhysicsState): number;

  getEndValue(): number;
  setEndValue(value: number): Spring;

  getVelocity(): number;
  setVelocity(value: number): Spring;

  getRestSpeedThreshold(): number;
  setRestSpeedThreshold(value: number): Spring;

  getRestDisplacementThreshold(): number;

  isOvershootClampingEnabled(): boolean;
  setOvershootClampingEnabled(value: boolean): Spring;

  isOvershooting(): boolean;

  advance(time: number, realDeltaTime: number): void;
  systemShouldAdvance(): boolean;

  notifyPositionUpdated(notifyActivate?: boolean, notifyAtRest?: boolean): void;

  wasAtRest(): boolean;
  isAtRest(): boolean;
  setAtRest(): Spring;

  interpolate(value: number): void;

  getListeners(): Array<Listener>;
  addListener(value: Listener): Spring;
  removeListener(value: Listener): Spring;
  removeAllListeners(): Spring;

  currentValueIsApproximately(value: number): boolean;
}

notifyPositionUpdated

be used in
advance
inlude onSpringUpdate
onSpringUpdate in  customer


advance

spring.addListener

addListener
   addListener: function(newListener) {
      this.listeners.push(newListener);
      return this;
    },
    

onSpringUpdate


```
 notifyPositionUpdated: function() {
      for (var i = 0, len = this.listeners.length; i < len; i++) {
        var listener = this.listeners[i];

          listener.onSpringUpdate(this);

      }
    },
```

SpringConfig .fromOrigamiTensionAndFriction

SpringConfig
 .fromOrigamiTensionAndFriction
 
 ```
 fromOrigamiTensionAndFriction: function(tension, friction) {
      return new SpringConfig(
        OrigamiValueConverter.tensionFromOrigamiValue(tension),
        OrigamiValueConverter.frictionFromOrigamiValue(friction));
    },

 ```
 
 SpringConfig   
 des:store  tension friction
 ```
   function SpringConfig(tension, friction) {
      this.tension = tension;
      this.friction = friction;
    };
 ```

springSystem.createSpring

createSpring
return Spring
params tension?: number, friction?: number
what is tension(n. 张力，拉力；紧张，不安；电压)  friction(n. 摩擦，[力] 摩擦力)
spring 
store a lot of property and methods
```
 createSpring: function(tension, friction) {
      var springConfig;
      if (tension === undefined || friction === undefined) {
        springConfig = SpringConfig.DEFAULT_ORIGAMI_SPRING_CONFIG;
      } else {
        springConfig =
          SpringConfig.fromOrigamiTensionAndFriction(tension, friction);
      }
      return this.createSpringWithConfig(springConfig);
    },
```
```
 createSpring: function(tension, friction) {
    springConfig =
          SpringConfig.fromOrigamiTensionAndFriction(tension, friction);
      return this.createSpringWithConfig(springConfig);
    },
```