Guide on accessing an element from a predicate object in Typescript while using Angular

Question

Guide on accessing an element from a predicate object in Typescript while using Angular

I'm trying to wrap my head around how to access an element that exists on an object of a specific type but is defined as a type predicate.

For example, let's say we have a Team defined as:

let team$: Observable<ErrorModel | Team>

The result of a successful call to this observable is of type Team, which has a code, while the ErrorModel does not. This leads Typescript linter to throw an error saying

code does not exist on type ErrorModel | Team

.

So essentially,

return team$.subscribe(response => {
    console.log(response.code);
}

How can I access response.code in this scenario? Even using typeof won't resolve the lint error.

typescript

Answer 1

Answer №1

When dealing with a response that can be either a Team or an ErrorModel, the compiler restricts access to only common properties of both types. To work around this, you can use a type guard to narrow down the type of the response. One way to do this is through an in type-guard:

team$.subscribe(response => {
  if ('code' in response) console.log(response.code);
});

Answer 2

When dealing with a response that can be either a Team or an ErrorModel, the compiler restricts access to only common properties of both types. To work around this, you can use a type guard to narrow down the type of the response. One way to do this is through an in type-guard:

team$.subscribe(response => {
  if ('code' in response) console.log(response.code);
});

Guide on accessing an element from a predicate object in Typescript while using Angular

Answer №1

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