Three ways of error handling in JS. * Return NULL * Throw Errors * Monad Either Find out which one suits for you.

1. E R RO R H A N D L I N G W / J S
F O N G

2. Return NULL
Throw Errors
Monad Either

3. Return NULL
Throw Errors
Monad Either

5. Vague Signature
Not Expressive
Caller Has No Clue

6. R E T U R N N U L L
• Requires caller to be aware of NULL
• Silent for caller
• Not expressive at all
• Vague Function Signature

7. Throw Errors
Monad Either
Return NULL

9. Deceive Signature
Break the flow
Easy to break

10. T H RO W E R RO R S
• Caller must handle it by try-catch
• Break the flow of caller
• Less expressive
• Deceive Function Signature
• Try-catch usually for interaction with external systems

11. G O A L S
• Honest and expressive signature
• Support a number of error types for caller
• Solid way to identify error types
• Don’t break the flow

12. G O L A N G WAY
• Encapsulate the result to an array
• Return the array
Reference: https://dev.to/oieduardorabelo/javascript-handling-errors-like-go-3efk

14. S T I L L A L I T T L E B I T
H A S S L E …

15. Throw Errors
Monad Either
Return NULL

16. F U N C T I O N A L P R O G R A M M I N G
• Functions are first-class citizens
• Expression > Statement
• Pure Function with no side effects

17. M O N A D
• A monad is a way of composing functions that require
context in addition to the return value, such as
computation, branching, or I/O.
• It is based on a simple symmetry — A way to wrap a
value into a context, and a way to unwrap the value
from the context

18. 🏣
" #
M O N A D
D ATAD ATA

19. Expressive
Flow & Solid
Chainable

20. 4 F E AT U R E S
• Map: apply functions to itself
• Context：package
• Type Lift：wrap
• Flatten：unwrap
→ Examples: Array, Promise,…

22. I N T R O D U C I N G E I T H E R

24. Always Left Always Right

26. M O R E P O W E R F U L I N
T RY P E S C R I P T…

27. source: https://gist.github.com/brunovegreville/1289eba4455de2413724c04d8eab3c78#file-either-ts

28. Various Error Types
Expressive Response

29. R E S O U R C E S
• JavaScript Monads Made Simple
• Type-Safe Error Handling In TypeScript
• Functional Error Handling with Express.js and DDD |
Enterprise Node.js + TypeScript
• Expressive error handling in TypeScript and benefits for
domain-driven design (medium star alert)
• Chapter 9: Monadic Onions