decorators.js

import { observable } from 'mobx'

class UIStore {
  @observable isSliderOpen = false;
  @observable isAccountDropdownOpen = false;

  constructor(state) {
    Object.assign(this, state)
  }
}

export default UIStore

no-decorators.js

import { extendObservable } from 'mobx'

class UIStore {
  constructor(state = {}) {
    extendObservable(this, {
      isSliderOpen: state.isSliderOpen || false,
      isAccountDropdownOpen: state.isAccountDropdownOpen || false,
    })
  }
}

export default UIStore