text: export class Spring {
    constructor({fromValue, toValue}) {
      this.toValue = toValue
      this.fromValue = fromValue
    }
    onUpdate(fn) {
      this.onUpdate_ = fn
      return this
    }
    onStop(fn) {
      this.onStop_ = fn
      return this
    }
    start() {
      this.onUpdate_({currentValue: this.toValue})
      this.onStop_()
    }
  }
  