Error Handling & Patterns
Either Pattern
Implement functional error handling using Either<Left, Right> data structures.
Last Updated: July 29, 2026
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10 min read
The Either pattern from functional programming represents values with two possibilities: Left (conventionally errors) or Right (conventionally success values).
1. Introduction & Architecture
2. Deep Dive & Core Concepts
Mnemonic: 'Right' is 'correct' (success value); 'Left' is the error payload.
3. Basic Code Example
4. Advanced Production Patterns
5. Interactive Code Playground
console.log("Either pattern provides functional Left/Right failure handling.");6. Common Pitfalls & Edge Cases
Note: Conventionally in functional programming,
Left holds failure details and Right holds success data.7. Interview Q&A & Quizzes
Q: What does 'Right' represent in the Either pattern?
A: By convention, Right represents successful values ('Right is correct').
8. Summary Comparison Table
| Side | Convention | Type |
|---|---|---|
Left | Error / Failure | Left |
Right | Success / Payload | Right |