Programming Typescript by Boris Cherny

About Book

This book is about how to put javascript on scale with type annotations. The best book to start using Typescript so far.

Notes

Types:

any: try not to use it

unknown: just don’t

boolean

number

bigint

string

symbol: use it rarely, mostly for string keys in objects or maps.

Objects: use it for structural typing

Arrays

Typles: Tuples are subtypes of array.

null: universal stuff

undefined: Variable that has not been assigned a value yet

void: Function that doesn’t have a return statment

never: function that never returns

enums: they are pretty shit https://www.youtube.com/watch?v=0fTdCSH_QEU

Declaring and Invoking Functions

// TODO

Gists

Compiler

Standard compiler:

Program is parsed into an AST.

AST is compiled to bytecode.

Bytecode is evaluated by the runtime.

Typescript:

💡

Type literal: A type that represents a single value and nothing else.

💡

Structural typing: A style of programming where you just care that an object has certain properties, and not what its name is (nominal typing). Also called duck typing in some languages (or, not judging a book by its cover).

Intermission: Type Aliases, Unions, and Intersections

Type aliases


type Age = number
type Person = {
 name: string
 age: Age
}


let age: Age = 55
let driver: Person = {
 name: 'James May'
 age: age
}

Union and intersection types


type Cat = {name: string, purrs: boolean}
type Dog = {name: string, barks: boolean, wags: boolean}
type CatOrDogOrBoth = Cat | Dog
type CatAndDog = Cat & Dog

// Cat
let a: CatOrDogOrBoth = {
 name: 'Bonkers',
 purrs: true
}
// Dog
a = {
 name: 'Domino',
 barks: true,
 wags: true
}
// Both
a: CatAndDog = {
 name: 'Donkers',
 barks: true,
 purrs: true,
 wags: true
}