Composing Software in JavaScript

Source: Eric Elliott's Composing Software series.

Workflow

1. Identify the coupling — is the problem inheritance, shared mutable state, or entangled side effects? See Composition Hierarchy below.
2. Choose the composition tool — pure function → factory → functional mixin → class (last resort). Use the Checklist below.
3. Apply the pattern — read the matching reference file for the concrete technique.
4. Verify — can the new unit be tested without mocks? Can it be reused without importing its collaborators?

Central thesis: all software design is composition — breaking problems down into small pieces and composing solutions back up. The choice of how to compose shapes everything about maintainability, testability, and flexibility.

Core Vocabulary