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Learn TypeScript 10x faster with AI

Paste the type error that's blocking you. Kuest helps you read it, asks what you meant the type to be, and explains how to fix it.

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4.87en iOS13,917,000+estudiantes ya estudian con Kuest

topics
9
Compiles to
JavaScript
Learn first
JavaScript
Used with
React, Node.js, Angular

See how Kuest teaches it

It asks before it tells, so you do the thinking and it sticks.

You: const user = users.find(u => u.id === id); console.log(user.name); gives 'user' is possibly 'undefined'. Why?
Kuest: Think about what find does when nothing matches. What does it return then?
You: Undefined, I think. If no user has that id there's nothing to return.
Kuest: Right, so its return type is User | undefined. What would happen at runtime if you read .name on undefined?
You: It would crash with a TypeError. So TypeScript is warning me before that happens.
Kuest: Exactly. How could you tell TypeScript you've handled that case?
You: Check first: if (!user) return; then user.name is safe. Or use user?.name if undefined is fine to log.

find returns T | undefined, so narrow with a check or ?. before using the result.

Students who lock in with Kuest

students
13,917,000+
App Store rating
4.87
countries
100+

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The method

How to study TypeScript with Kuest

TypeScript makes sense once your JavaScript is solid, so learn the types on top of code you already understand. Read compiler errors slowly from the first line, ask what type you expected versus what TypeScript inferred, and practice narrowing and generics on small examples until they feel natural.

  1. Build on your JavaScriptTutor chat

    Ask how a JavaScript pattern you know is typed, like an object, a callback or a fetch call.

  2. Decode type errorsSnap a photo

    Paste the error and the code around it, or snap your editor, and Kuest helps you read what TypeScript is telling you.

  3. See how types relateTeaching board

    Use the teaching board to diagram unions, narrowing and generic type parameters flowing through a function.

  4. Predict the typeQuizzes

    Answer quizzes that ask what type a variable has after a check, or whether a line compiles.

  5. Keep the syntax handyFlashcards

    Review utility types, generics syntax and tsconfig options as spaced flashcards.

  6. Work on your blind spotsGap finder

    Let Kuest find the topics you keep getting wrong, like generics or narrowing, and practice those.

What you'll cover

Tap a topic to learn it now.

  1. 01Why types and the compilerExplain what tsc checks and how TypeScript compiles to JavaScript
  2. 02Basic types and annotationsAnnotate variables, parameters and return values and let inference do the rest
  3. 03Objects, type aliases and interfacesDescribe object shapes with type and interface and choose between them
  4. 04Union types and narrowingCombine types with | and narrow them with typeof, in and equality checks
  5. 05null, undefined and strict modeHandle possibly undefined values with checks, ?. and ?? instead of !
  6. 06Functions and overloadsType callbacks, optional parameters and functions that return different types
  7. 07GenericsWrite reusable functions and types with <T> and constraints like extends
  8. 08Utility typesTransform types with Partial, Pick, Omit and Record
  9. 09Typing real projectsType React props, API responses and modules and configure tsconfig.json

Try asking

Tap a question and Kuest starts teaching it, step by step.

Helps you prepare for

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