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typescript2.txt
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typescript2.txt
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1) Utility type: Record
const ids: Record<number, string> = {
1: 'a',
2: 'b',
};
2) null colision : ??
3) MutationFunction:
export type MutationFunction = (v: number) => number;
export function arrayMutate(numbers: number[], mutate: MutationFunction): numbers[] {
return numbers.map(mutate)
}
const myNewMutateFunc: MutationFunction = (v: number) => v * 200;
console.log( arrayMutate([1,20,30], (v) => v * 10))
4) Function overloading:
interface ICoordinate {
x: number;
y: number;
}
function parseCoordinate(obj: ICoordinate): ICoordinate;
function parseCoordinate(str: string): ICoordinate;
function parseCoordinate(x: number, y: number): ICoordinate;
function parseCoordinate(arg1: unknown, arg2?: unknown): ICoordinate {
let coord: ICoordinate = {
x: 0,
y: 0,
};
if (typeof arg1 === 'object') {
coord = {
...(arg1 as ICoordinate),
};
} else if (typeof arg1 === 'string') {
(arg1 as string).split(',').forEach((str) => {
const [key, value] = str.split(':');
coord[key as 'x' | 'y'] = parseInt(value, 10);
});
} else {
coord = {
x: arg1 as number,
y: arg2 as number,
};
}
return coord;
}
console.log(parseCoordinate(10, 20));
console.log(parseCoordinate({ x: 10, y: 20 }));
console.log(parseCoordinate('x:10, y:20'));
5) Resolve JSON file: for importing json file in ts
tsconfig:
"resolveJsonModule": true
6) Optional callback:
function addWithCallback(x: number, y: number, callback?: () => void) {
callback?.();
}
7) Tuples: Array of values
function simpleStringState(initial: string): [() => string, (v: string) => void] {
let str: string = initial;
return [
() => str,
(v: string) => {
str = v;
}
]
}
const [strGetter, strSetter] = simpleStringState("hello");
console.log(strGetter());
strSetter("Good bye")
console.log(strGetter());
8) Generics:
function simpleStringState<T>(initial: T): [() => T, (v: T) => void] {
let str: T = initial;
return [
() => str,
(v: T) => {
str = v;
}
]
}
const [strGetter, strSetter] = simpleStringState("hello");
const [strGetter, strSetter] = simpleStringState<string | null>(null);
9) KeyOf:
function pluck<DataType, KeyType extends keyof DataType>(items: DataType[], key: KeyType): DataType[KeyType][] {
return items.map(item => item[key]);
}
const dogs = [
{name: "micro", age: 3},
{name: "max", age: 5}
];
console.log(pluck(dogs, 'name'))
console.log(pluck(dogs, 'age'))
-------------------------------------
interface BaseEvent {
time: number;
user: string;
}
interface EventMap {
addToCart: BaseEvent & { quantity: number , productID: string};
checkout: BaseEvent;
}
function sendEvent<Name extends keyof EventMap>(name: Name, data: EventMap[Name]): void {
console.log([name, data]);
}
sendEvent("addToCart", {productID: 'foo', user: 'baz', quantity: 1, time: 10});
sendEvent("checkout", {time: 20, user: "boo"});
10) Utility types:
a) Partial: makes all properties optional
interfce MyUser {
name: string;
id: string;
email?: string;
}
const merge = (user: MyUser, overrideUser: Partial<MyUser>): MyUser => {
return {...user, ...overrideUser}
}
b) Required : makes all properties required
type RequiredMyUser = Required<MyUser>
c) Pick<Type, Keys>: takes only mentioned properties
type JustEmailAndName = Pick<MyUser, "email" | "name">; // {email?: string | undefined; name: string;}
d) Omit: opposite of pick
const mapById = (user: MyUser[]): Record<MyUser["id"], Omit<MyUser, "id">> => {
return users.reduce((a, v) => {
const {id, ...others} = v;
return {
...a,
[id]: others
}
})
}
e) Readonly:
interface Cat {
name: string; breed: string; }
function makeCate(name: string, breed: string): Readonly<Cat> {
return { name, breed
}; }
const cat = makeCat("Random", 'fab'); cat.name = "sdfdsf" // error not possible
For tuple
function makeCoordinates(x: number, y: number) : readonly [number, number] { return [x, y]; }
use const
const values = [10,30,50] as const; // you cannot reset the values
f) Parameters & ReturnType
type Name = {
first: string;
last: string;
}
function addFullName(name: Name): Name & {
fullName: string;
} {
return {
...name,
fullName: `${name.first} ${name.last}`
}
}
function permuteRows<T extends (...args:any[])=>void>(iteratorFunc: T, data: Parameters<T>[0][]): ReturnType<T>[] {
return data.map(iteratorFunc);
}
console.log(permuteRows(addFullName, [{first: "jack", last: "hill"}]))
g) ConstructorParameters & InstanceType
class PersonFullName {
constructor(public name: Name) { }
get fullName() {
return `${this.name.first} ${this.name.last}`
}
}
function createObject<T extends new (...args:any[])=>void>(objectType: T, data: ConstructorParameters<T>[0][]): InstanceType<T>[] { return data.map((item) => new objectType(item)); }
console.log(createObject(PersonFullName, [{first: "jack", last: "hill"}]).map(obj => obj.fullName))
11) Mapped Types:
type MyFlexibleDogInfo = {
name: string;
} & Record<string, string>;
OR
type MyFlexibleDogInfo = {
name: string;
[s: string]: string | number;
}
const dog: MyFlexibleDogInfo = {
name: "Abcd",
breed: "Xyz",
age: 12
};
interface DogInfo {
name: string;
age: number;
}
type OptionsFlags<Type> = {
[Property in keyof Type]: null;
};
type DogInfoOptions = OptionsFlags<DogInfo>; // {name: null, age: null}
-------------------------------------------------------------------------------------------------
type KeyTypes<T> = {
[K in keyof T]-?: K extends string ? string
K extends number ? number
K extends symbol ? symbol : never
}[keyof T];
-------------------------------------------------------------------------------------------------
Important:
Create dynamic typed properties with template literals:
type Listeners<Type> = {
[Property in keyof Type as `on${Capitalize<string & Property>Change}`]?: (
newValue: Type[Property]
) => void; } & {
[Property in keyof Type as `on${Capitalize<string & Property>Delete}`]?: (
newValue: Type[Property]
) => void; };
function listenToObject<T>(obj: T, listeners: Listeners<T>): void {
throw "Needs to be implemented"
}
const lg: DogInfo = {
name: "LG",
age: 13
}
type DogInfoListeners = Listeners<DogInfo>;
listenToObject(lg, {
onNameChange: (v: string) => {},
onAgeChange: (v: string) => {},
onNameDelete: (v: string) => {},
onAgeDelete: (v: string) => {},
})
12) Abstract
abstract class StreetFighter {
move() {}
flight() {
console.log(this.attack());
}
abstract attack(): string;
}
class Ryu extends StreetFighter {
attack() {
return "bom";
}
}
const ryu = new Ryu();
ryu.flight();
13) Mixins
Create functions from function , but also now create classes from functions
function myLogFunction() {
return (str: string) => {
console.log(str)
}
}
const logger = myLogFunction();
logger('Log string');
function createLoggerClass() {
return class MyLoggerClass {
private completelog: string = "";
log(str: string) {
console.log(str);
this.completelog += str + '\n';
}
dumpLog() {
return this.completelog;
}
}
}
const MyLogger = createLoggerClass();
const logger2 = new MyLogger();
logger2.log("foo");
logger2.dumpLog();
function CreateSimpleMemoryDatabase<T>() {
return class SimpleMemoryDatabase {
private db: Record<string, T> = {};
set(id: string, value: T) {
this.db[id] = value;
}
get(id: string) : T {
return this.db[id];
}
getObject(): object {
return this.db;
}
}
}
const StringDatabase = CreateSimpleMemoryDatabase<string>();
const sdb1 = new StringDatabase();
sdb1.set("a", "foo");
sdb1.get("a")
type Constructor<T> = new (...args: any[]) => any;
function Dumpable<T extends Constructor<{
getObject(): object;
}>>(Base: T) {
return class Dumpable extends Base {
dump() {
console.log(this.getObject())
}
}
}
const DumpableStringDatabase = Dumpable(StringDatabase);
const sdb2 = new DumpableStringDatabase();
sdb2.set("jack", "hello jack");
sdb2.dump();
18) Condition types:
interface PokemonResults {
count: number;
next?: string;
previous?: string;
results: {
name: string;
url: string;
}[];
}
type FetchPokemonResult<T> = T extends undefined
? Promise<PokemonResults[]>
: void;
function fetchPokemon<T extends undefined | ((data: PokemonResults) => void)>(
url: string,
cb?: T
): FetchPokemonResult<T> {
if (cb) {
fetch(url)
.then((r) => r.json())
.then(cb);
return undefined as FetchPokemonResult<T>;
} else {
return fetch(url).then((resp) => resp.json()) as FetchPokemonResult<T>;
}
}
// fetchPokemon(https://pokeapi.co/api/v2/pokemon?limit=10, (data) => {
// data.results.forEach(pokemon => console.log(pokemon.name))
// });
(async function() {
const data = <PokemonResults>(await fetchPokemon(https://pokeapi.co/api/v2/pokemon?limit=10));
data.results.forEach(pokemon => console.log(pokemon.name))
})()
------------------------------------------------------------------------------------------
interface dog {
name: string;
}
interface cat {
age: number;
}
type animal = dog | cat;
const a: animal = {
age: 25
}
type z<T> = T extends dog ? dog & {petname: string} : cat & {jump: number}
const h = a as z<typeof a>;
console.log(h.age); // h.name will get error