TypeScript Utility Types

interface Todo {
    title: string;
    description: string;
}

type subTodo = Partial<Todo>

const todo1: subTodo = {
    title: 'This is a title'
}

const todo2: subTodo = {
    description: 'This is a description'
}

interface Todo {
    title?: string;
    description?: string;
}

const todo1: Todo = {
    title: 'This is a title'
}

const todo2: Todo = {
    description: 'This is a description'
}

const todo3: Required<Todo> = { // 'description' is declared here.
    title: '123'
}

interface Todo {
		title: string;
}

const todo: Readonly<Todo> = {
		title: 'This is a title'
}

todo.title = 'new title' // Cannot assign to 'title' because it is a read-only property.

interface Todo {
    title: string;
}

type TodoList = 'todo1' | 'todo2' 

const todos: Record<TodoList, Todo> = {
    todo1: { title: 'todo1' },
    todo2: { title: 'todo2' }
}

interface Todo {
    title: string;
    description: string;
    done: boolean;
}

type TodoPreview = Pick<Todo, 'title' | 'done'> 

const todo: TodoPreview = {
    title: 'title',
    done: true
}

interface Todo {
    title: string;
    description: string;
    done: boolean;
}

type TodoPreview = Omit<Todo, 'description' | 'done'> 

const todo: TodoPreview = {
    title: 'title'
}

type Todo = string | number | (() => void)

type TodoPreview = Exclude<Todo, string> 
// type TodoPreview = number | (() => void)

type Todo = string | number | (() => void)

type TodoPreview = Extract<Todo, string> 
// type TodoPreview = string

type Todo = NonNullable<number | string | null | undefined>
// tyoe Todo = <number | string>

type T0 = Parameters<() => string>
// type T0 = []

type T1 = Parameters<(s: string) => void>
// type T1 = [s: string]

type T0 = ConstructorParameters<ErrorConstructor>;
// type T0 = [message?: string]

type T1 = ConstructorParameters<FunctionConstructor>;
// type T1 = string[]

type T2 = ConstructorParameters<RegExpConstructor>;
// type T2 = [pattern: string | RegExp, flags?: string]

type T3 = ConstructorParameters<any>;
// type T3 = unknown[]

type T0 = ReturnType<() => string>
// type T0 = string

class C {
  x = 0;
  y = 0;
}

type T0 = InstanceType<typeof C>;  // C

type T1 = InstanceType<any>;  // any

type T2 = InstanceType<never>;  // any