title: Angular 8: Array .map() .slice() No funcionan
body: <p>Angular 8 with Firebase: Array .map () .slice () Do not work.
  Hi.
  I have been trying to make a copy of an array using .map () and .slice () in Angular 8, but using these methods I find that the copied array still has the reference to the original array.</p>
  
  <p>I don't know if I'm doing it wrong, or these methods don't work in Angular 8.</p>
  
  <pre><code> // Iniciamos la escucha de los cambios de la data del usuario
      if (!this.$userData) {
        this.$userData = this.userService.user().valueChanges().subscribe(data =&gt; {
          if (data) {
            this.userData = Object.assign({}, data);
            const temp = data.operationsList.map((x) =&gt; {
              x.bank = 'Popular';
              return x;
            });
            console.log(this.userData.operationsList, temp);
            if (!this.userData.validated) {
              this.router.navigate(['register/pendingValidation']);
            }
          }
        });
      }
  </code></pre>
  
  <p>console.log:</p>
  
  <pre><code>(2) [{…}, {…}]
  0: {bank: "Popular", commission: 0, country: "ve", countryAllowed: "all", maximum: 0, …}
  1: {bank: "Popular", commission: 0, country: "ve", countryAllowed: "all", maximum: 0, …}
  
  (2) [{…}, {…}]
  0: {bank: "Popular", commission: 0, country: "ve", countryAllowed: "all", maximum: 0, …}
  1: {bank: "Popular", commission: 0, country: "ve", countryAllowed: "all", maximum: 0, …}
  </code></pre>
  
  <p>When modifying the copied array, the changes are also reflected in the original array.</p>