Overview The andTee and orTee methods allow you to perform side effects on Ok or Err values without affecting the Result. Useful for logging, metrics, or other operations that shouldn’t fail your main logic.
Signatures andTee class ResultAsync < T , E > { andTee ( f : ( t : T ) => unknown ) : ResultAsync < T , E > }
f
(t: T) => unknown
required
Function to execute if Ok. Can be sync or async. Errors are caught and ignored.
orTee class ResultAsync < T , E > { orTee ( f : ( e : E ) => unknown ) : ResultAsync < T , E > }
f
(e: E) => unknown
required
Function to execute if Err. Can be sync or async. Errors are caught and ignored.
Returns: The original ResultAsync unchangedUsage Logging success const result = await fetchUser ( id ) . andTee ( user => console . log ( 'Fetched user:' , user . name )) . andThen ( validateUser ) . andTee ( user => console . log ( 'Validated user:' , user . id )) // Logs are printed, but don't affect the Result chain
Logging errors const result = await processData ( input ) . orTee ( async error => { await sendErrorToMonitoring ( error ) console . error ( 'Process failed:' , error ) }) . orElse ( handleError )
Metrics collection const result = await apiCall () . andTee (() => metrics . increment ( 'api.success' )) . orTee (() => metrics . increment ( 'api.failure' ))
Audit trail const processOrder = ( order : Order ) => { return validateOrder ( order ) . andTee ( async () => { await auditLog . write ( 'ORDER_VALIDATED' , order . id ) }) . andThen ( chargePayment ) . andTee ( async () => { await auditLog . write ( 'PAYMENT_CHARGED' , order . id ) }) }
Error handling in tee functions If the tee function throws an error or rejects, the error is caught and ignored . The original Result passes through unchanged.
const result = await okAsync ( 5 ) . andTee (() => { throw new Error ( 'This error is ignored' ) }) // result is still Ok(5)
Key characteristics Feature andTee orTee Runs on Ok values Err values Affects Result No No Error handling Errors ignored Errors ignored Return value Original ResultAsync Original ResultAsync Async support Yes Yes
Comparison with through methods // andTee - errors ignored, value preserved const tee = await okAsync ( user ) . andTee ( logUser ) // If logUser fails, continues . andThen ( saveUser ) // Type: ResultAsync<User, SaveError> // andThrough - errors propagate, value preserved const through = await okAsync ( user ) . andThrough ( validateUser ) // If validate fails, chain stops . andThen ( saveUser ) // Type: ResultAsync<User, ValidationError | SaveError>
through-methods Side effects that can fail the chain
Result tee methods Synchronous version