Do TypeScript types run in the browser?

No. They are erased and do not execute.

What type should untrusted JSON have?

unknown until a parser proves a domain type.

Does HttpClient.get () validate the response?

No. It only annotates the intended successful body.

What does HttpClient.get () guarantee?

Only that you intend the successful body to be Course[] — you must still validate

The compiler will parse the body

Angular will reject malformed JSON automatically as a type error at runtime

TypeScript Tutorial 0/102 lessons ~6 min read Lesson 102“Type-safe frontend to enterprise architecture”

TypeScript Quiz

Q: How should catch (error) be typed?

unknown, then narrow before you inspect the value.

Check compile-time versus runtime thinking, unknown boundaries, configuration, and architecture judgments with instant feedback.

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Focus

10 guided sections

Practice signal

Examples included

Career prep

Interview Q&A included

Introduction

This knowledge check covers the TypeScript course: erasure, unknown, configuration, APIs, and architecture. Submit each answer for an explanation, then finish for a score.

How to Use This Quiz

Answer every question, read the explanation even when you are correct, then finish for a score. Treat a miss as a pointer back to the matching lesson, not as a trivia failure.

What This Quiz Covers

The mix includes compile-time versus runtime, unknown, configuration, HTTP generics, type guards, and architecture judgments that appear in interviews.

Compile Time Versus Runtime

A correct TypeScript answer names what the checker proves and what JavaScript still does after emit. If you claim a type validates JSON, revisit the compiler and validation lessons.

Trust Boundaries

HTTP, queues, files, and environment variables change origin. Those values start as unknown and become trusted only after runtime validation.

Configuration and Strictness

strict, noUncheckedIndexedAccess, and incremental project references change what the checker assumes. They do not replace tests or parsers.

Architecture Judgments

Shared contracts, catch typing, and check-time performance are design choices. Prefer the smallest public surface that preserves a real invariant.

Scoring and Review

Aim to explain every miss in one sentence that distinguishes a compile-time guarantee from a runtime control. Then retake only the weak areas.

Interview Use

Use these prompts as spoken drills. A staff answer includes a definition, a failure mode, and a production placement.

Quiz

TypeScript knowledge check

16 questions · answer each one and get instant feedback.

Progress: 0/16Score: 0

1What happens to TypeScript types in emitted JavaScript?

They become runtime instanceof checks
They are erased and do not execute
They are stored in a hidden WeakMap
They make JavaScript run faster

2Which type should you use for untrusted JSON before validation?

any
object
unknown
Record<string, any>

3What does HttpClient.get<Course[]>() guarantee?

The JSON is an array of Course
The compiler will parse the body
Only that you intend the successful body to be Course[] — you must still validate
Angular will reject malformed JSON automatically as a type error at runtime

4When is a string literal union usually better than a numeric enum?

Never — enums are always safer
When you need a closed vocabulary without a runtime reverse-mapping object
When you want implicit conversion from any number
When you need the values to exist only at runtime

5What does noUncheckedIndexedAccess change?

Array.push return type
Index reads become T | undefined
Objects become immutable
Modules resolve differently

6Which statement about const is true?

const freezes nested objects
const prevents reassignment of the binding
const is a runtime type
const removes properties from the type

7What is the sound use of a user-defined type guard?

Return true for every object
Promise more in the predicate than the implementation checks
Check every fact the predicate claims
Cast and return true

8Why does satisfies exist?

To assert any value to a type
To check compatibility while keeping the inferred literal type
To skip strictNullChecks
To emit runtime validation

9Where should environment variables be typed?

As string everywhere because process.env values are always present
Parsed once at startup into a Config object
As any in each file
Only in the frontend bundle

10What is a trust boundary?

A TypeScript namespace
A place where data or control changes origin and must be validated
A private class field
A tsconfig include path

11Which option improves checker performance without dropping safety?

transpile-only CI
Project references and incremental builds
Replacing unknown with any
Disabling strictNullChecks

12What should a shared contract package contain?

Every React prop type in the company
Stable commands, events, and versioned DTOs
ORM entity classes
Express Request extensions only

13How should catch (error) be typed?

error: Error
error: any
error: unknown, then narrow
error: string

14Name the TypeScript type for values that are not yet proven.

Hint: we look for key terms in your answer.

15Which compiler flag bundle enables noImplicitAny and strictNullChecks together?

Hint: we look for key terms in your answer.

16Write the type predicate return type for a function that proves value is a string.

Hint: we look for key terms in your answer.

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