Intersection type syntax in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an intersection type in TypeScript?

An intersection type combines multiple types into one. It means a value must satisfy all the combined types at the same time.

beginner

How do you write an intersection type in TypeScript?

Use the ampersand (&) symbol between types. For example: type A = Type1 & Type2;

intermediate

What happens if two intersected types have conflicting properties?

TypeScript will require the property to satisfy both types. If conflicts can't be resolved, it causes a type error.

beginner

Example: What does this type mean? <br>type Person = { name: string } & { age: number };

It means a Person must have both a name (string) and an age (number).

intermediate

Can intersection types combine interfaces and types?

Yes, you can intersect interfaces and type aliases together using & to create a new combined type.

Which symbol is used for intersection types in TypeScript?

A |

B &

C +

D *

The ampersand (&) symbol is used to combine types into an intersection type.

What does this intersection type require? <br>{a: number} & {b: string}

A An object with both a and b

B An object with a or b but not both

C An object with either a or b

D An object with neither a nor b

Intersection means the object must have both properties a and b.

Can intersection types be used to combine primitive types like string & number?

A Yes, it creates a union

B No, it creates an array

C Yes, it creates a tuple

D No, it results in never type

Intersecting incompatible primitive types like string & number results in the never type, meaning no value can satisfy both.

If two intersected types have the same property with different types, what happens?

A TypeScript picks the first type

B TypeScript picks the second type

C TypeScript throws a type error

D TypeScript ignores the property

Conflicting property types in intersection cause a type error because no value can satisfy both.

Which of these is a valid intersection type?

A type T = {x: number} & {y: string};

B type T = {x: number} | {y: string};

C type T = {x: number} + {y: string};

D type T = {x: number} - {y: string};

Only the ampersand (&) is valid for intersection types.

Explain in your own words what an intersection type is and how it is used in TypeScript.

Think about how two sets overlap and what belongs to both.

Describe a situation where using an intersection type would be helpful in a program.

Imagine you want an object that has features from two different things.