Utility Types: Partial, Pick, Omit & Record

TypeScript ships a set of utility types that build new types out of ones you already have, instead of writing everything from scratch. Four of the most common: Partial, Pick, Omit, and Record.

interface Task {
  id: string;
  title: string;
  done: boolean;
  priority: 'low' | 'medium' | 'high';
}

type TaskDraft = Partial<Omit<Task, 'id'>>;
// every field optional, and 'id' isn't part of the type at all

function updateTask(task: Task, changes: TaskDraft): Task {
  return { ...task, ...changes };
}

updateTask({ id: '1', title: 'Write lesson', done: false, priority: 'high' }, { done: true });

The four utility types

Partial<Omit<Task, 'id'>> above composes two of them: drop id entirely, then make what's left optional, exactly what an "update" function needs, callers shouldn't be able to change a task's id, and shouldn't have to repeat every other field just to change one.

Record for lookup tables

const board: Record<Task['priority'], Task[]> = {
  low: [],
  medium: [],
  high: [],
};

board.low.push({ id: '2', title: 'Sort backlog', done: false, priority: 'low' });

Task['priority'] reads the type of the priority property directly off Task, so board is guaranteed to have exactly the three keys the union allows, no more, no less. Try board.urgent and the compiler rejects it before the code runs.