Q:

How to do combineLatest operator in valueChanges subscriptions

showDateCriteria = combineLatest(this.myForm.controls['name'].valueChanges, this.myForm.controls['age'].valueChanges, (name, age) => ({name, age}))
.subscribe(val => !(val.name==null ||val.age==null ));

I have tried this code with combineLatest Operator and showDateCriteria 
<div *ngIf="{{showDateCriteria | async}}">Show This</div>

I am unable to show the <div> eventhough particular condition is satisfied
https://stackblitz.com/edit/angular-rs3d7a

A:

As the error says ERROR Error: InvalidPipeArgument: '[object Object]' for pipe 'AsyncPipe'.
You're trying to async pipe a subscription, which doesn't make sense.
You should pipe streams.
this.showDateCriteria =
    combineLatest(
        this.myForm.controls['name'].valueChanges,
        this.myForm.controls['age'].valueChanges, (name, age) => ({
            name,
            age
        }));
this.showDateCriteria.subscribe(val => !(val.name == null || val.age == null));

EDIT: 
You should also startWith, otherwise the combineLatest will not trigger.
Also, the logic was wrong, you should return boolean true when either of them is not null, like so:
this.showDateCriteria = combineLatest(
    this.myForm.controls['name'].valueChanges.pipe(startWith(null)),
    this.myForm.controls['age'].valueChanges.pipe(startWith(null)),
    (name, age) => {
        console.log(name);
        return name || age;
    });

https://stackblitz.com/edit/angular-g6vi6k?file=src%2Fapp%2Fapp.component.ts

