Developer Path Predefined learning modules Programming TypeScript

TypeScript

What you'll learn?

Description: You can use features of TypeScript required for work with frameworks built on top of it.

Person who successfully completed a requirement for given block can:

deliver simple and typical functionalities with little to no additional help,
present the problem and explored solutions clearly and in detail when asking for help,
leverage the most commonly used standard library’s capabilities.

Areas

Data types

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Learn about available data types in TypeScript.

Learn

📗 Primitive types
📗 Arrays
📗 Functions
📗 Object types
📗 Type aliases
📗 Interfaces
📗 Union Types
- TypeScript Handook on Union types
- TypeScript Deep Dive on Discriminated unions
📗 null and undefined
📗 Never and void

Interview

What are primitive types?

How to define an array of types? How is it different with tuple?

How to access type of array element? How about accessing type of tuple elements?

What is type alias?

What is an interface?

What are the differences between type alias and interface?

How to define function in an interface?

How to define function in a type alias?

What are function overloads? What are they used for? How can we declare these - show three different ways?

What are literal types and when they are useful?

What’s the difference between never and void?

What difference does it make to have strictNullChecks option turned on?

Type Compatibility and Guards

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Read on compatibility between different types and structures and learn about narrowing down types using various methods.

Learn

📗 Type Compatibility
📗 Narrowing types
📗 Type guards

Interview

How can we narrow down different types? Tell me about and give examples on:

Truthiness,

typeof operator,

in operator,

instanceof operator,

type predicates,

discriminated unions.

Utility types

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Get familiar with some of the utility types.

Learn

📗 Utility Types

Interview

Tell me about Extract/Exclude and Omit/Pick - how they are different from each other?

Tell me about Partial/Required - what are they doing? What is their use case?

How can we access type of parameters in function? How do we extract type of n-th parameter?

How can we access type of return value in function?

What other utility types do you know?

Generics

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How to make use of generics (named templates in other languages sometimes).

Learn

📗 TS Handbook on Generics
📗 TS Deep Dive on Generics

Interview

How to define generic type?

How to define multiple generic types?

How to define default generic value?

How to apply constraints on possible generic values?

Katas

Create a class that makes use of a generic. It should accept anything as a constructor and have following methods:

getValue - its return type should be derived from generic,

setValue - its argument should be derived from generic.

Create a function that makes use of a generic. Return type of this function should be derived from generic.

Create an interface for a function that accepts object as a first argument and second argument MUST be one of the keys in this obejct.

Conditional types

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Get familiar with assigning types conditionally and extract types from function parameters, return types and promise resolve values.

Learn

📗 Conditional Types

Interview

How to use conditional types? When they are useful?

What does infer keyword do?

Katas

Create a type conditional where you extract value from given Promise<Type> type.

Mapped and indexed types

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Learn how to transform types from one structure to another.

Learn

📗 keyof type operator
📗 typeof type operator
📗 Indexed access
📗 Mapped Types
📗 Template Literal Types

Interview

What does keyof operator do? What’s use case for it?

What does typeof operator do in TypeScript context? How it is different from JavaScript runtime?

How to access nested fields in a object type?

Explain what is mapped type and what it is useful for?

Katas

Create an interface which as a type variable accepts a union and creates properties from elements of this union (property type can be anything, for example string).

Create an interface type which as a type variable accepts an object type where this object values are functions. Returned type should have the same keys, but object value should be value of a function provided under that key. Example: { foo: () => number } should transform to { foo: number }

Create a static object where it’s values are different class constructors (e.g. Dog, Cat, Bird). Then create a function that accepts one of the keys of this object as an argument and returns instance of class under this key.

Create a function that:

Accepts two parameters: field name that starts with email_{AnyNumberHere} and field value which is any string; Hint: use template literals.

Returns an object where field name is a key and field value is value.

For a harder version of this task you can try restricting negative numbers from {AnyNumberHere} placeholder; you can try using type-fest library.

Summary

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It is highly recommended that you read whole TypeScript Handbook and TypeScript Deep Dive (linked below) for a better understanding of TypeScript.

Learn

📗 TypeScript Handbook
📗 TypeScript Deep Dive

Katas

Solve excersises 1-10 (with extras) and 15 (optionally) from typescript excersises (you don’t need to put it on github or anywhere, solving them on this page only is fine).