Design Principles

How functions, modules, data and state are shaped. System structure lives in architecture-guidelines; code-level quality rules in coding-practices.

Always

• Logic lives in pure functions with explicit parameters; a thin wrapper reads configuration and performs the effect.
• Return new values instead of mutating inputs; mark unmutated parameters and fields readonly.
• Accept small interfaces and pass dependencies in; no inheritance for reuse.
• Data is plain objects plus functions; classes only for stateful services, no getters or setters.
• Read the clock once per operation and pass the value down.
• One cancellation handle (ctx, AbortSignal) flows through the whole operation; never start a fresh one mid-chain.
• Pick maps and sets for lookups, arrays and slices for sequences; hand out copies of internal collections.
• Importing a module does no I/O and reads no environment; compute lazily.

References