<form method="post" [formGroup]="registerForm" (ngSubmit)="onSubmit()">
<input type = text name="first_name">

const user = {
          first_name: this.registerForm.controls.first_name.value,
          last_name: this.registerForm.controls.last_name.value,
          email: this.registerForm.controls.email.value,
          c_email: this.registerForm.controls.c_email.value,
          password: this.registerForm.controls.password.value,
          c_password: this.registerForm.controls.c_password.value,
          birth_date: this.registerForm.controls.birth_date.value,
          phone: this.registerForm.controls.phone.value,
          timezone: this.registerForm.controls.timezone.value,
        };