Mastering TypeScript: Advanced Patterns

Use inference where it helps, lock it where it matters

A good type system guides users. A bad one becomes a puzzle. My rule: infer in APIs, enforce in core layers.

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type Result<T> =
  | { ok: true; value: T }
  | { ok: false; error: string };
function wrap<T>(fn: () => T): Result<T> {
  try {
    return { ok: true, value: fn() };
  } catch {
    return { ok: false, error: "Failed" };
  }
}

Leverage template literal types

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type EventName = `user.${"created" | "updated" | "deleted"}`;

When you have event-driven systems, this prevents impossible events from slipping through.

Use discriminated unions for workflow state

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type FlowState =
  | { status: "idle" }
  | { status: "loading"; startedAt: number }
  | { status: "success"; finishedAt: number }
  | { status: "error"; message: string };

It forces every consumer to handle each state explicitly.