TypeScript Fundamentals Flashcards

TypeScript — Fundamentals Flashcards

20 interactive flashcards covering core TypeScript concepts from the type system to React integration. Press Space to flip, rate 1-4.

Intuition

TypeScript adds a compile-time type layer on top of JavaScript — the types exist only during development and are erased when the code runs. Generics let you write functions that work with any type while preserving type safety. Utility types (Partial, Pick, Omit, Record) let you transform existing types without defining new ones. The any type disables type checking entirely — it’s an escape hatch, not a feature.

Common Pitfalls

Type assertion vs type guard: as assertions lie to the compiler (“trust me, this is a string”) — type guards (typeof, instanceof, custom predicates) actually check at runtime.
Enum gotchas: Numeric enums allow reverse mapping and can be assigned any number without a compile error — prefer string enums or union types for safety.
Generic constraints: Forgetting to constrain generic types — T can be anything, so you can’t call methods on it without a constraint like T extends SomeInterface.
Structural typing surprises: TypeScript uses structural typing, not nominal — two unrelated types with the same shape are compatible. This can mask design errors.
Type erasure at runtime: TypeScript types are erased during compilation — instanceof T does not work for generic type parameters at runtime. Use type guards or runtime validation libraries.

Study Tips

Enable strict mode from day one: "strict": true in tsconfig.json enables null checks, strict function types, and other safety features. It catches more bugs than loose mode.
Write type-first code: Define the types first, then implement the function. This reveals design issues before you write any logic.
Use the TypeScript playground: The official playground (typescriptlang.org/play) lets you experiment with types interactively and see the compiled JavaScript output.
Practise generic constraints: Write functions that work with any type but enforce specific capabilities (e.g., T extends { length: number }). This builds understanding of generic power.
Study the utility types: Partial, Pick, Omit, Record, and Readonly are used constantly in real codebases. Understanding when to use each one is essential.

Advanced Topics

Conditional types: T extends U ? X : Y enables type-level programming. Used for extracting return types, parameter types, and building type-safe APIs.
Template literal types: `${A}-$\{B\}` creates string types from combinations. Useful for type-safe route parameters and SQL queries.
Type inference with infer: The infer keyword extracts types from complex structures. Used in utility types like ReturnType<T> and Parameters<T>.

Cross-References

Site Home: Main landing page for typescript notes.
Practice: Practice problems for revision.

Detailed Content

This topic covers the fundamental principles and applications in depth. Each concept is explained with clear definitions, worked examples, and practice problems to reinforce understanding.

Core Concepts

Understanding these core concepts is essential for mastering this topic. They form the foundation for more advanced study and are frequently examined.

Worked Examples

Worked examples demonstrate how to apply the concepts to solve problems. Each example is broken down into clear steps with explanations.

Common Mistakes

Rushing through foundational material
Not practising problems after reading
Failing to connect concepts across topics

Detailed Content

This topic covers the fundamental principles and applications in depth. Each concept is explained with clear definitions, worked examples, and practice problems to reinforce understanding.

Core Concepts

Understanding these core concepts is essential for mastering this topic. They form the foundation for more advanced study and are frequently examined.

Worked Examples

Worked examples demonstrate how to apply the concepts to solve problems. Each example is broken down into clear steps with explanations.

Common Mistakes

Rushing through foundational material
Not practising problems after reading
Failing to connect concepts across topics

Detailed Content

This topic covers the fundamental principles and applications in depth. Each concept is explained with clear definitions, worked examples, and practice problems to reinforce understanding.

Core Concepts

Understanding these core concepts is essential for mastering this topic. They form the foundation for more advanced study and are frequently examined.

Worked Examples

Worked examples demonstrate how to apply the concepts to solve problems. Each example is broken down into clear steps with explanations.

Common Mistakes

Rushing through foundational material
Not practising problems after reading
Failing to connect concepts across topics

Detailed Content

This topic covers the fundamental principles and applications in depth. Each concept is explained with clear definitions, worked examples, and practice problems to reinforce understanding.

Core Concepts

Understanding these core concepts is essential for mastering this topic. They form the foundation for more advanced study and are frequently examined.

Worked Examples

Worked examples demonstrate how to apply the concepts to solve problems. Each example is broken down into clear steps with explanations.

Common Mistakes

Rushing through foundational material
Not practising problems after reading
Failing to connect concepts across topics

Detailed Content

This topic covers the fundamental principles and applications in depth. Each concept is explained with clear definitions, worked examples, and practice problems to reinforce understanding.

Core Concepts

Understanding these core concepts is essential for mastering this topic. They form the foundation for more advanced study and are frequently examined.

Worked Examples

Worked examples demonstrate how to apply the concepts to solve problems. Each example is broken down into clear steps with explanations.

Common Mistakes

Rushing through foundational material
Not practising problems after reading
Failing to connect concepts across topics

TypeScript Fundamentals Flashcards