Intersection type syntax in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this TypeScript code using intersection types?

Consider the following TypeScript code. What will be logged to the console?

Typescript

type A = { x: number };
type B = { y: string };

const obj: A & B = { x: 10, y: "hello" };
console.log(obj.x, obj.y);

A undefined undefined

B Type error: Property 'y' is missing

C 10 hello

D 10 undefined

💡 Hint

An intersection type combines all properties from both types.

The variable 'obj' must have both properties 'x' and 'y'. So accessing obj.x and obj.y prints 10 and 'hello'.

🧠 Conceptual

intermediate

Which statement best describes intersection types in TypeScript?

Choose the correct description of intersection types (&) in TypeScript.

A They create a type that has properties from both types combined.

B They create a type that can be either one type or the other.

C They remove common properties from both types.

D They create a union of all possible values from both types.

💡 Hint

Think about combining properties, not choosing one or the other.

Intersection types combine all properties from both types, so the resulting type has everything from both.

🔧 Debug

advanced

What error does this TypeScript code raise?

Analyze this code snippet and select the error it produces.

Typescript

type C = { a: number } & { a: string };
const val: C = { a: 5 };

A Type error: Type 'number' is not assignable to type 'string'.

B Syntax error: Invalid intersection type.

C No error, val is valid.

D Runtime error: Cannot assign number to string.

💡 Hint

Check the property 'a' types in both intersected types.

The property 'a' is declared as number in one type and string in the other. Intersection requires both, which is impossible, so TypeScript errors.

📝 Syntax

advanced

Which option correctly declares an intersection type for two interfaces?

Select the correct syntax to declare a variable with intersection type of interfaces X and Y.

Typescript

interface X { id: number; }
interface Y { name: string; }

A let obj: X && Y = { id: 1, name: "Alice" };

B let obj: X | Y = { id: 1, name: "Alice" };

C let obj: X, Y = { id: 1, name: "Alice" };

D let obj: X & Y = { id: 1, name: "Alice" };

💡 Hint

Intersection uses '&' symbol between types.

The '&' symbol combines types to require all properties. Option D uses correct syntax.

🚀 Application

expert

How many properties does the variable 'data' have after this code runs?

Given these types and variable, how many properties does 'data' have?

Typescript

type T1 = { a: number; b: string };
type T2 = { b: string; c: boolean };

const data: T1 & T2 = { a: 5, b: "hello", c: true };

A 4

B 3

C 1

D 2

💡 Hint

Intersection merges all properties, duplicates count once.

The intersection type combines all properties from T1 and T2. Property 'b' appears in both but counts once. So properties are 'a', 'b', and 'c' = 3 total.