ArrayEnum.md

tags	typescript arrays tuples enums
topic	Arrays, Tuples & Enums
status	done

ArrayEnum.ts — Arrays, Tuples, Enums

Source: typescript/src/ArrayEnum.ts

Code

// Basic dtype arrays
const chaiFlavours: string[] = ["masala", "ginger"]
const chaiPrices: number[] = [20, 25]

const rating: Array<number> = [4.5, 5.0]

type Chai = {
    name: string;
    price: number;
}

// Arrays of custom dtypes
const menu: Chai[] = [
    {name: "Masala", price: 20},
    {name: "Ginger", price: 25}
]

// readonly array
const cities: readonly string[] = ["Delhi", "Jaipur"]
// cities.push("Pune") // Property 'push' does not exist on type 'readonly string[]'.

// Multidimensional Arrays
const table: number[][] = [
    [1,2,3],
    [4,5,6]
]

// Tuples
let chaiTuple: [string, number]
chaiTuple = ["Masala", 2] // order should strictly be same

let userInfo: [string, number, boolean?]
userInfo = ["Amit", 100] // boolean is optional

const location: readonly [number, number] = [23.45, 12.24] // readonly tuple
const chaiItems: [name: string, price: number] = ["Masala", 20] // named tuples, more preferred

// enum
enum CupSize {
    SMALL,
    MEDIUM,
    LARGE
}

const size = CupSize.LARGE

// customizing enums
enum Status {
    PENDING = 100,
    SERVED, // 101
    CANCELLED // 102
}

enum ChaiType {
    MASALA = "masala",
    GINGER = "ginger"
}
function MakeChai(type: ChaiType){
    console.log(`Making ${type}`)
}

MakeChai(ChaiType.GINGER)
// MakeChai("masala") // Argument of type '"masala"' is not assignable to parameter of type 'ChaiType'.

// Heterogenous values, not used in production
enum RandomEnum {
    ID = 1,
    NAME = "chai"
}

// Constant enums
const enum Sugar {
    LOW = 1,
    MEDIUM = 2,
    HIGH = 3
}

const s = Sugar.HIGH

// Unexpected Behavior
let t: [string, number] = ["chai", 10]
t.push("Extra") // Here it gives no error as tuple is an array itself and items can be pushed into an array

Arrays

Syntax	Example
type[]	string[]
Array<type>	Array<number>
readonly type[]	readonly string[]

[!quote] TypeScript Docs "To specify the type of an array like [1,2,3], use the syntax number[]; you may also see Array<number>."

Tuples

• Fixed-length, typed-per-position arrays.
• Named tuples: [name: string, price: number] — preferred.

[!warning] Tuple .push() Caveat t.push("Extra") doesn't error! Tuples are arrays at runtime. Use readonly to prevent this.

Enums

Enum Type	Starting Value	Example
Numeric	0 (auto)	SMALL = 0
Numeric (custom)	User-set	PENDING = 100
String	User-set	MASALA = "masala"
Const	Inlined	const enum Sugar

[!quote] TypeScript Docs "Enums allow a developer to define a set of named constants."

See also: [[interface]], [[generics]], [[objectsTS]]