Type query

typeof, instanceof

Any type

“Refinement”, “Classes Declare Both Values and Types”

Keys

keyof

Object types

“The keyof operator”

Property lookup

O[K]

Object types

“The keying-in operator”

Mapped type

[K in O]

Object types

“Mapped Types”

Modifier addition

+

Object types

“Mapped Types”

Modifier subtraction

-

Object types

“Mapped Types”

Read-only modifier

readonly

Object types, array types, tuple types

“Objects”, “Classes and Inheritance”, “Read-only arrays and tuples”

Optional modifier

?

Object types, tuple types, function parameter types

“Objects”, “Tuples”, “Optional and Default Parameters”

Conditional type

?

Generic types, type aliases, function parameter types

“Conditional Types”

Nonnull assertion

!

Nullable types

“Nonnull Assertions”, “Definite Assignment Assertions”

Generic type parameter default

=

Generic types

“Generic Type Defaults”

Type assertion

as, <>

Any type

“Type Assertions”, “The const type”

Type guard

is

Function return types

“User-Defined Type Guards”