Satisfies operator in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using satisfies operator?

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

Typescript

const config = {
  host: "localhost",
  port: 8080,
  secure: false
} satisfies { host: string; port: number; secure: boolean };

console.log(config.port);

A 8080

B TypeError at runtime

C "localhost"

D Compilation error

💡 Hint

The satisfies operator checks type compatibility but does not change runtime values.

The satisfies operator ensures the object matches the specified type but does not affect the actual value. The code logs the port number 8080.

❓ Predict Output

intermediate

What error does this code raise?

What error will this TypeScript code produce when using the satisfies operator incorrectly?

Typescript

const user = {
  name: "Alice",
  age: "25"
} satisfies { name: string; age: number };

console.log(user);

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

B Runtime error: Cannot read property 'name' of undefined

C No error, logs the user object

D Syntax error: Unexpected token 'satisfies'

💡 Hint

Check the type of the age property compared to the expected type.

The satisfies operator enforces that the object matches the type. Here, age is a string but expected to be a number, causing a type error.

🔧 Debug

advanced

Why does this code fail to compile?

This TypeScript code uses the satisfies operator but fails to compile. What is the reason?

Typescript

const settings = {
  theme: "dark",
  notifications: true
} satisfies { theme: string; notifications: boolean; language: string };

console.log(settings);

A Type mismatch: 'notifications' should be a string.

B Missing property 'language' in object but required by type.

C Runtime error: 'settings' is undefined.

D No error, code compiles and logs the object.

💡 Hint

Check if all required properties in the type are present in the object.

The satisfies operator requires the object to have all properties of the type. 'language' is missing, causing a compile error.

🧠 Conceptual

advanced

What is the main benefit of the satisfies operator?

Which statement best describes the main benefit of using the satisfies operator in TypeScript?

A It removes properties from an object at compile time.

B It converts a variable to a different type at runtime.

C It narrows the type of a variable without changing its runtime value.

D It forces a variable to be readonly at runtime.

💡 Hint

Think about how satisfies affects type checking versus runtime behavior.

The satisfies operator checks that a value matches a type but does not change the value or its runtime behavior.

❓ Predict Output

expert

What is the type of 'data' after this assignment?

Given the following TypeScript code using the satisfies operator, what is the inferred type of the variable data?

Typescript

const data = {
  id: 1,
  name: "Item",
  tags: ["a", "b"]
} satisfies Readonly<{ id: number; name: string; tags: string[] }>;

// What is the type of 'data' here?

A "data" is a mutable object with no type constraints.

B "data" is of type Readonly<{ id: number; name: string; tags: string[] }> with all properties readonly.

C "data" is of type any because satisfies removes type information.

D "data" is of type { id: number; name: string; tags: string[] } but readonly properties are not enforced.

💡 Hint

The satisfies operator checks compatibility but does not change the inferred type or readonly status.

The satisfies operator ensures the object matches the type but does not make the variable readonly. The inferred type is the object literal type, not readonly.