Observable Errors
Learn how to catch errors in an Observable stream, including how to use catchError within an Observable stream itself.
Observable exceptions
What happens when something goes wrong within an Observable stream?
Obviously, we will need a mechanism to catch these errors so that we can do something sensible with them.
As an example of a faulty Observable stream, consider the following code:
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// Interface definition for a property 'value' of type numberinterface IValue {value: number}// Interface definition for an optional property 'id' of type IValueinterface INestedObj {id?: IValue;}// Create an observable 'objEmit' of type INestedObj and initialize it with 3 objectsconst objEmit : Observable<INestedObj> = of({ id: { value: 1 } }, // First object with id and value property{}, // Second object with no properties{ id: { value: 2 } } // Third object with id and value property);
Here, we start with two interfaces named IValue
and INestedObj
.
-
The
IValue
interface on lines 2 – 4 has a property namedvalue
of typenumber
. -
The
INestedObj
interface on lines 7 – 9 has a single optional parameter namedid
of typeIValue
. -
We then create an Observable named
objEmit
on lines 12–16 that emits three values:- The first value has the nested structure described by the
INestedObj
interface. - The second
- The first value has the nested structure described by the
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