TL;DR(short answer):

your method salvarImagem doesn’t return anything(explicit salvarImagem(): void) and looking on your code you should return an object with the property datahoje

Longer answer:

To avoid error you either need to return value

salvarImagem(): { datahoje: Date } {
  ...
  return { datahoje };
}

or call the method and take value from an object which you have edited(as a side effect)

this.selecionado['dataInicial']

A bit about Typescripts’ types:

https://www.typescriptlang.org/docs/handbook/basic-types.html

Also, your IDE “knows” return type – you can check it by ctrl(cmd for MacOS) + hovering over the method.

Well, it happens that I have some code made with angular bootstrap which is a data picker, which is inside an event party register(which you click new and make a new event) and I want the user to choose a date and save it, here goes the code of the date picker:

  <p>Selecione a data</p>

                    <ngb-datepicker #dp [startDate]="modelAtual" [(ngModel)]="modelAtual" (navigate)="date = $event.next"></ngb-datepicker>

                            <pre>Month: {{ date.month }}.{{ date.year }}</pre>
                            <pre>Model: {{ model | json }}</pre>

and then I have the code to save the info of the date, which is in typescript:

  salvarImagem() {
    if (this.chave === undefined) {
      let dat1=new Date().getMilliseconds();
      const filePath = `/eventos/${dat1}-${this.selecionado["lastModified"]}` + '.' + this.selecionado['tipoarquivo'];
      const fileRef = this.storage.ref(filePath);
      const task = this.storage.upload(filePath, this.file);
      let datahoje = new Date(this.modelAtual.year,this.modelAtual.month,this.modelAtual.day).getTime();
      this.selecionado['dataInicial']=datahoje;
      var horario = this.time.hour + ':'+ this.time.minute;
      this.selecionado['horaInicial']=horario; 



      // observe percentage changes
      this.uploadPercent = task.percentageChanges();
      // get notified when the download URL is available
      task.snapshotChanges().pipe(
        finalize(() => {
          this.downloadURL = fileRef.getDownloadURL();
          this.downloadURL.toPromise().then(du => {

            this.selecionado["arquivo"] = du;

            this.service.add(this.selecionado);

            this.router.navigate(['/eventos']);
            alert("Objeto salvo");

          });
        })
      ).subscribe();

    } else {
      this.service.update(this.chave, this.selecionado);
      this.router.navigate(['/estabelecimentos']);
      alert("Objeto salvo");
    }
  }

and then I have the code that loads whenever the user wants to edit this register (which you can do) and in order to show exactly the date he chooses before, I try to assign the variable modelAtual to the variable datahoje, that for some reason returns the error mentioned in the title

if (this.chave !== undefined) {
  this.service.get(this.chave).valueChanges().subscribe(obj => {
    this.selecionado = obj;
    this.logo = this.selecionado["arquivo"];
    //this.modelAtual = { year: 2011, month: 7, day:23};
    this.modelAtual = this.salvarImagem().datahoje;

  })
}

would anyone be able to tell me the cause of that?