react-spring/src/animated/AnimatedTracking.js

Animate React with ease

import Animated from './Animated'

export default class AnimatedTracking extends Animated {
  constructor(value, parent, animationClass, animationConfig, callback) {
    super()
    this._value = value
    this._parent = parent
    this._animationClass = animationClass
    this._animationConfig = animationConfig
    this._callback = callback
    this.__attach()
  }

  __getValue() {
    return this._parent.__getValue()
  }

  __attach() {
    this._parent.__addChild(this)
  }

  __detach() {
    this._parent.__removeChild(this)
  }

  update = throttle(() => {
    this._value.animate(
      new this._animationClass({
        ...this._animationConfig,
        to: this._animationConfig.to.__getValue(),
      }),
      this._callback
    )
  }, 1000 / 30)
}

function throttle(callback, limit) {
  var wait = false
  return function() {
    if (!wait) {
      callback.call()
      wait = true
      setTimeout(() => (wait = false), limit)
    }
  }
}