TypeScript Basics Test

Test your understanding of annotations, inference, interfaces, unions and safe unknown values.

6 questions. Choose the best answer for each question, then review every explanation.

Question 1 of 6

1 of 6

Question 1Which declaration explicitly requires a number?

let count = "3" as any;let count: string = "3";const count = null;let count: number = 3;

Question 2What is an interface commonly used to describe?

An HTML documentThe shape of an objectA runtime database tableA compiled JavaScript loop

Question 3What values can this variable accept?

let id: string | number;

Only stringsOnly numbersEvery possible valueStrings or numbers

Question 4What does the question mark mean on this property?

interface User { nickname?: string }

The property must be nullThe property is optionalThe property is privateThe property is readonly

Question 5What type does TypeScript infer here?

const active = true;

The literal type truestringnumberany

Question 6Why is unknown generally safer than any?

It disables JavaScript outputIt automatically validates network dataIt must be narrowed before most operationsIt accepts only strings