Build a typed task list

Build a command-line task list that reads and writes a JSON file.

Start with a state model that prevents impossible combinations:

type TaskStatus = 'open' | 'completed'

type Task = {
  id: number
  title: string
  status: TaskStatus
}

Support four commands: add, list, complete, and remove. Give every function a clear input contract. Let local return types infer unless an exported boundary needs an explicit promise.

Treat the JSON file as unknown. Validate the top-level array and every task field before returning Task[]. A type assertion does not count as parsing.

Add this helper only if it preserves useful information:

function findById<T extends { id: number }>(items: T[], id: number) {
  return items.find(item => item.id === id)
}

The result keeps the caller’s specific item type and includes undefined when no item matches.

Test these failure paths:

• the file does not exist
• the JSON is malformed
• one task has a string ID
• an unknown command is passed
• a requested task does not exist

Keep strict enabled and add a repeatable check:

npx tsc --noEmit

Finish by removing any any, unjustified assertion, or non-null assertion. The goal is not to make the checker quiet. The goal is to make every uncertain boundary and missing value explicit.