How to run the method only after the previous function has ended

Question

I have the code below, but the method showVideo() is executed and follows the execution at the same time of the code below it, without waiting for the showVideo() is due to simultaneous execution the value set in the Storage is not correct.

buscaBonus() {

     this.servicoGeral.showVideo(); //esse metodo chama o `addTempo()` que por 
     sua vez chama um localStorage.setItem para setar o tempo ganho, e o código 
     abaixo recupera esse valor para mostrar em tela. Só deveria executar o 
     código abaixo após o `showVideo()`.

     if (localStorage.getItem("segundos") == undefined) {
       this.totalBonus = localStorage.getItem("segundos");
     }    

     let alert = this.alertCtrl.create({
      title: 'Você ganhou 5 segundos de bônus!',
      message: 'Poderá utilizar e até acumular para jogar qualquer fase.',
      buttons: [
        {
          text: 'Entendi ',
          handler: () => {
            return true;
          }
        }
      ],
      enableBackdropDismiss: false
      });    
      alert.present();      
    }

     showvideo(): Promise<boolean>{    
        const rewardVideoConfig: AdMobFreeRewardVideoConfig = {
          id: 'ca-app-pub-1390341047819209/6782590495',
          isTesting: true,
          autoShow: true
        }

        this.admobFree.rewardVideo.config(rewardVideoConfig);
        return new Promise<boolean>((resolve) => {

          rewardVideoClose = this.admobFree.on(this.admobFree.events.REWARD_VIDEO_CLOSE).subscribe(() => {

          });
          rewardVideoReward = this.admobFree.on(this.admobFree.events.REWARD_VIDEO_REWARD).subscribe(() => {
            this.addTempo();
            rewardVideoReward.unsubscribe();
          });

          this.admobFree.rewardVideo.prepare()
            .then(() => { })
            .catch(() => {
              loading.dismiss();
              resolve(false);
            });
        }); 
     } 
      addTempo() {
         if (localStorage.getItem("segundos") == null) {
           this.tempoSegundos = 5
         } else {
           let tempo = localStorage.getItem("segundos");
           this.tempoSegundos = (parseInt(tempo) + 5)
         }
         let tempo: string;
         tempo = this.tempoSegundos.toString()
         localStorage.setItem('segundos', tempo);
     }

Answer 1

What would be the first function you perform?

Try to call the this.addTempo()as in this example, using a callback.

funcao() {
  let loader = this._loaderCtrl.create();
  loader
    .present()
        .then(() => {
           .subscribe(
              () => {
              let toast = this._toastCtrl.create({
                message: "mensagem",
                duration: 3000
              });
              toast.onDidDismiss(() => {
                this.addTempo()
              });
          toast.present();
        loader.dismiss();
 }

Example with loading:

loader.dismiss(()=>{
    this.addTempo()
 });

Answer 2

You can create a barrier, same method used in asynchronous requests, at a glance, maybe I can help you.

var simpleBarrier = require('simple-barrier'),
fs = require('fs');

// create a barrier instance
var barrier = simpleBarrier();

// load some files, let the barrier handle the callbacks:
fs.readFile('foo.txt', barrier.waitOn());
fs.readFile('bar.txt', barrier.waitOn());
fs.readFile('baz.txt', barrier.waitOn());

// add a callback for when all files are loaded
barrier.endWith(function( results ){

   // Results is an array of the values given by fs.readFile
   // the array is in the order that barrier.waitOn() was called, regardless of the 
   // order they were loaded in
   console.log('foo, bar, and baz are:', results.join('\n'));
});

Source: https://github.com/jimhigson/simple-barrier