How intersection combines types in Typescript - Quick Revision & Summary

Recall & Review

beginner

What does an intersection type do in TypeScript?

An intersection type combines multiple types into one. The new type has all properties and methods from each combined type.

beginner

How do you write an intersection type in TypeScript?

Use the & symbol between types. For example: type A = B & C; means A has all properties of B and C.

intermediate

What happens if two intersected types have properties with the same name but different types?

TypeScript requires the property to satisfy both types. If they conflict, the intersection becomes impossible to satisfy and causes an error or results in the never type.

beginner

Example: What properties does this type have?<br>type A = {name: string};<br>type B = {age: number};<br>type C = A & B;

Type C has both name (string) and age (number) properties. It combines all properties from A and B.

intermediate

Can intersection types combine primitive types like string & number?

No. Intersection of incompatible primitive types like string & number results in never, meaning no value can satisfy both.

What symbol is used to create an intersection type in TypeScript?

A &

B |

C +

D *

The & symbol combines types into an intersection type.

If type A = {x: number} and type B = {y: string}, what properties does A & B have?

A Only x

B Only y

C Both x and y

D Neither x nor y

Intersection combines all properties, so it has both x and y.

What happens if two intersected types have the same property name but different types?

A TypeScript merges them as a union

B TypeScript picks the first type

C TypeScript ignores one property

D TypeScript throws an error or results in never

Conflicting property types cause an error or never type.

What is the result of string & number in TypeScript?

A never

B number

C string

D string | number

Intersection of incompatible primitives results in never.

Which of these is a valid intersection type?

A type C = {a: number} + {b: string};

B type C = {a: number} & {b: string};

C type C = {a: number} | {b: string};

D type C = {a: number} - {b: string};

Only & creates intersection types.

Explain in your own words how intersection types combine multiple types in TypeScript.

Think about how two sets of properties join together.

Describe what happens when two intersected types have the same property name but different types.

Consider if a property must be both a string and a number at the same time.