Removing modifiers with minus in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the minus (-) modifier do in TypeScript mapped types?

It removes a specific modifier (like readonly or optional) from properties in a mapped type.

beginner

How do you remove the readonly modifier from all properties of a type T?

Use { -readonly [P in keyof T]: T[P] } to create a new type without readonly modifiers.

intermediate

What is the difference between +readonly and -readonly in mapped types?

+readonly adds the readonly modifier, while -readonly removes it.

intermediate

Can you remove the optional modifier from properties in a mapped type? How?

Yes, by using -? after the property name, like { [P in keyof T]-?: T[P] }.

beginner

Example: What does this type do?<br>

type Mutable<T> = { -readonly [P in keyof T]: T[P] }

It creates a new type from T where all properties are mutable (not readonly).

Which syntax removes the readonly modifier from properties in a mapped type?

A { [P in keyof T]-?: T[P] }

B { -readonly [P in keyof T]: T[P] }

C { readonly [P in keyof T]: T[P] }

D { +readonly [P in keyof T]: T[P] }

The minus sign before readonly removes the readonly modifier.

How do you remove the optional modifier from properties in a mapped type?

A { [P in keyof T]-?: T[P] }

B { -readonly [P in keyof T]: T[P] }

C { +readonly [P in keyof T]: T[P] }

D { [P in keyof T]?: T[P] }

The minus question mark (-?) removes the optional modifier.

What does this mapped type do?<br>

type Readonly<T> = { +readonly [P in keyof T]: T[P] }

A Removes optional modifier from all properties

B Removes readonly modifier from all properties

C Adds readonly modifier to all properties

D Adds optional modifier to all properties

+readonly adds the readonly modifier to properties.

Which modifier removes the optional flag from a property in a mapped type?

A +?

B +readonly

C -readonly

D -?

The -? removes the optional modifier from properties.

If you want to make all properties mutable (not readonly), which syntax is correct?

A { -readonly [P in keyof T]: T[P] }

B { +readonly [P in keyof T]: T[P] }

C { [P in keyof T]-?: T[P] }

D { [P in keyof T]+?: T[P] }

Removing readonly with -readonly makes properties mutable.

Explain how to remove the readonly and optional modifiers from all properties of a TypeScript type using mapped types.

Think about using minus signs before modifiers inside the mapped type.

Describe the difference between adding and removing modifiers in TypeScript mapped types and give examples.

Focus on the plus and minus signs before modifiers.