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Discussion on: Angular: Setters vs ngOnChanges - which one is better?

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Replies for: ngOnChanges({ name, email }: SimpleChanges) { const username = name.currentValue || email.currentValue; this.username$.next(username); } ...

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Giancarlo Buomprisco Author •

Hi! do you mean that name or email could be undefined? TBH I'd never ship this to production - just needed a short example with multiple inputs 😅

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Bo Vandersteene •

Ok so if you have a component that uses your code like this

<my-component [email]="email$ | async" 
                               [username]="username$ | async"> </my-component>

If the input of the observables look like this

email$    = -E----
username$  =  ----U--

Then the ngOnChanges will be called first with only email and then with only username so one of the two is undefined. Only the values that are changed are submitted in the SimpleChanges