如何告诉Typescript在这种情况下*函数的返回类型永远不会为null

Question

I'm trying to get typescript strictNullChecks working in an Angular 5 project.

I have a form:

this.signinForm = this.fb.group({
  emailAddress: ['', NGValidators.isEmail()],
  password: ['', Validators.required],
  rememberMe: false,
});

I can get the rememberMe control using this.signinForm.get('rememberMe') . The return of the FormGroup#get method however, is AbstractControl | null AbstractControl | null so typescript doesn't like this.signinForm.get('rememberMe').value (because it thinks this.signinForm.get('rememberMe') could be null).

Is it possible to tell typescript that, in this instance , the return of this.signinForm.get('rememberMe') is always AbstractControl and not AbstractControl | null AbstractControl | null ?

Answer 1

Use the ! operator:

this.signinForm.get('rememberMe')!.value

Answer 2

We can force type in TypeScript by wrapping expression with as [type] . In your case it would be (this.signinForm.get('rememberMe') as AbstractControl).value .