async_await_explanation.js

class A{
  saveArea(callback){
    const {t} = this.props;

    new Api('/nurses/area').post(this.prepareData())
    .then(response => {
      if(response.status === 200){
        response.json().then(json => {
          this.setState({
            popupTitle: t('area.success.title'),
            popupDescription: t('area.success.description'),
            popupVisibility: true
          });
          callback(,,,)
        })
      }else if(response.status === 422){
        this.setState({
            popupTitle: t('area.failure.title'),
            popupDescription: t('area.failure.description'),
            popupVisibility: true
          });
      }
    })
}
}

const a = new A()
a.saveArea(() =>  {...})  #undefined

###############################################################################################################
class A{
  async saveArea(){
    const {t} = this.props;

    const response = await new Api('/nurses/area').post(this.prepareData())
    if(response.status === 200){
      const json = await response.json()
      this.setState({
        popupTitle: t('area.success.title'),
        popupDescription: t('area.success.description'),
        json: json,
        popupVisibility: true
      });
    }else if(response.status === 422){
      this.setState({
          popupTitle: t('area.failure.title'),
          popupDescription: t('area.failure.description'),
          popupVisibility: true
      });
    }
    return json
  }
}


async function init(){
  const a = new A()
  const result =  a.saveArea()((result) => {...})  #Promise
}


init()