JS Ninjas Test

Front

Which of the following is a valid TypeScript data type? Options: number, bigint, symbol, all of the above

Back

all of the above

Answer explanation

TypeScript supports number, bigint, and symbol as valid data types.

Front

What does the 'readonly' keyword do in TypeScript?

Back

Makes a variable immutable and prevents reassignment.

Answer explanation

readonly' ensures the value cannot be modified after initialization.

Front

Which utility type makes all properties of a TypeScript interface optional? Options: Partial<T>, Required<T>, Readonly<T>, Pick<T, K>

Back

Partial<T>

Answer explanation

Partial<T> makes all properties optional.

Front

What is the difference between 'interface' and 'type' in TypeScript?

Back

Interfaces can be extended, types cannot; Types allow unions, interfaces do not.

Answer explanation

Interfaces can be extended and types support unions.

Front

Which of the following is a new JavaScript feature introduced in ES2022? Top-level await, Private class fields, Optional chaining, WeakRef

Back

Top-level await

Answer explanation

Top-level await was introduced in ES2022.

Front

What does 'as const' do in TypeScript?

Back

Makes the variable a readonly tuple, freezes the object, and makes it a literal type.

Answer explanation

as const' ensures values are inferred as literals and readonly.

Front

What is a difference between '==' and '===' in JavaScript?

Back

'===' checks type and value, '==' does type coercion.

Answer explanation

==' performs type coercion while '===' does not.

Front

What is the output of 'console.log(typeof null)' in JavaScript?

Back

object

Answer explanation

Due to legacy reasons, typeof null returns 'object'.

Front

What is the main advantage of using TypeScript over JavaScript?

Back

Static typing

Answer explanation

TypeScript provides static typing for better maintainability.

Front

Which of the following can be used for narrowing types in TypeScript? Options: typeof, instanceof, in, All of the above

Back

All of the above

Answer explanation

Type narrowing can be done using typeof, instanceof, and in.