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--- wiki2:new_typescript [2022/11/02 12:13]
alfred
+++ wiki2:new_typescript [2022/11/03 09:30] (actual)
@@ Línea 1: / Línea 1: @@
 ====== TypeScript ======
-<code typescript>
+  * {{ :wiki2:js:typescript:typescript-cheat-sheets.zip |Cheatsheets}}, from [[https://www.typescriptlang.org/cheatsheets]]
-/*
-Inicializar un paquete:
-npm init -y
-Añadir el compilador typescript
-npm add -s typescript
-Ejecutar el compilador typescript
-npx tsc
-Inicializar projecto typescript con codigo en src y salida en lib
-npx tsc --init --rootdir src --outdir lib
-Ahora la ejecución compila el codigo
-npx tsc
-Dejarlo compilando
-npx tsc --watch
-*/
-let message: string = "Hello world";
-console.log(message);
-/*
-"use strict";
-let message = "Hello world";
-console.log(message);
-*/
-//-- Primitives
-let isPresent: boolean = true;
-let beast: number = 66.4566;
-let anotherNumber: string = beast.toPrecision(1);
-let notDefined: undefined = undefined;
-let notPresent: null = null;
-let penta: symbol = Symbol('star');
-let biggy: bigint = 9007199254740991n;
-//-- List classes
-let array: Array<number> = [1, 2, 3];
-let array2: number[] = [1, 2, 3];
-let set: Set<number> = new Set([1, 2, 3]);
-//-- Generics
-class Queue<T> {
-    private data: Array<T> = [];
-    push(item: T) { this.data.push(item); }
-    pop(): T | undefined { return this.data.shift(); }
-}
-let queue: Queue<number> = new Queue();
-queue.push(33);
-//-- Tuples
-let tuple: [number, number] = [0, 0]; // [0, 0, 0] is an error
-//-- Types and type alias
-let center: {x: number, y: number} = {
-    x: 0, y: 0
-};
-type Point = {x: number, y: number};
-let center2: Point = {x: 0, y: 0};
-//-- Functions
-function add(a: number, b: number): number { return a + b; }
-function log(message: string): void { console.log(message); }
-function sum(...values: number[]) {}
-let addFunction: (a: number, b: number) => number;
-addFunction = add;
-//-- Structural typing
-type User = { id: string };
-type Product = { id: string };
-let user: User = { id: "1" };
-let product: Product = { id: "3" } ;
-let user2: User = product; // No error
-type Point2D = { x: number, y: number };
-type Point3D = { x: number, y: number, z: number};
-let p2: Point2D = { x: 0, y: 0 };
-let p3: Point3D = { x: 1, y: 1, z: 1 };
-p2 = p3; // No error. p3 = p2 <- error
-function takePoint2D (point: Point2D) {}
-takePoint2D(p3);
-//-- Classes
-class Animal {
-    private name: string;
-    protected position: number;
-    #last_name: string;  // This is also private, but `private` is prefered
-    constructor(name: string) {
-        this.name = name;
-        this.position = 0;
-        this.#last_name = "Toby";
-    }
-    public move(meters: number): void { this.position += meters; }
-}
-class Bird extends Animal {  // Having private position would not work
-    fly (miles: number): void { this.position += (miles * 0.0006); }
-}
-let cat = new Animal("cat");
-cat.move(10);
-//-- Any and Unknown
-let exampleAny: any = 333;
-let exampleUnknown: unknown = 333;  // safer
-exampleAny.allow.anything();
-let bBoolean: boolean = exampleAny;
-// exampleUnknown.does.not.allow();
-// exampleUnknown.trim(); // does not allow this either
-if (typeof exampleUnknown == 'string') { exampleUnknown.trim() }
-//-- Type assertion and casts
-import { load } from "./test.js"  // we require to "allowJS" in tsconfig.json
-let varLoaded = load();
-const trimmed: string = (varLoaded as string); // assertion
-let strVariable: string = "1992";
-let numVariable: number = +strVariable; // cast
-let bVariable: boolean = (numVariable == 1992);
-/*
-When you want to use an external variable, like process.env from node. We will do a declaration:
-declare const process: any;
-There is a way to directly define those external variables in a non invasive way:
-- You can set them in `env.d.ts` file.
-But if you are going to use node typing, the best way is to install the `@types/node` package.
-With this, it is not required to import those variables.
-For example, with Express.js: `@types/express`
-However, for using TypeScript on node we will make use of ts-node package.
-JS:
-If you create this class:
-class Person {
-    growOld() { this.whatever }
-}
-And you use a person instance with: const growOld = person.growOld(), `this` is lost.
-For maintaining the `this` context growOld must be defined like this:
-class Person {
-    growOld = () => { this.whatever }
-}
-*/
-//-- Readonly
-type XValue = {
-    readonly x: number;
-}
-let xvalue: XValue = {x: 33}
-// xvalue.x = 33; this gives an error
-//-- Unions
-function format(input: string | string[]) : void {} // Accepts string or string array
-//-- Literals
-let direction: 'North' | "South" | "East" | "West";
-direction = 'North';
-// direction = 'north'; error
-class Cat { meow() {}}
-class Dog { bark() {}}
-type Pet = Cat | Dog;
-let pet: Pet = new Cat()
-if (pet instanceof Cat) pet.meow();
-//-- Discrimination
-type Circle = {
-    kind: 'circle',  //This can be a boolean. The real example is with isValid: true, and then isValid: False
-    validatedValue: string,
-};
-type Square = {
-    kind: 'rectangle',
-    errorReason: string,
-};
-type Figure =
-    | Circle
-    | Square;
-function logResult(result: Figure) {
-    if (result.kind == 'circle') {
-        console.log('Success, validated value:', result.validatedValue);
-    }
-    if (result.kind == 'rectangle') {
-        console.error('Failure, error reason:', result.errorReason);
-    }
-}
-//-- parameter properties
-class Person {
-    constructor (public name: string, public age: number) {}
-}
-const adam = new Person('Adam', 12000);
-console.log(adam.name); // Prints Adam
-//-- Intersection types
-type Another2D = {
-    x: number,
-    y: number
-}
-type Another3D = Another2D & {
-    z: number
-}
-let aP3D = {x: 2, y: 3, z: 4}
-type AnotherPerson = { name: string }
-type Email = { email: string}
-function contact(data: AnotherPerson & Email) {}
-contact({name: "hola", email: "a@b.com"})
-type ContactData = AnotherPerson & Email;
-function contact2(data: ContactData) {}
-//-- Optionals
-type APerson = {name: string, email: string, phone?: string };
-const alfred: APerson = {name: "alfred", email: "a@a.com"}
-//-- Not null
-type Position = {x: number, y?: number | null | undefined}
-let p: Position = {x: 33}
-console.log(p.y!)
-//-- Interfaces
-interface Location2D  {
-    x: number,
-    y: number
-}
-interface Location2D {  // this is merged
-    xy: string
-}
-interface Location3D extends Location2D {
-    z: number
-}
-let location: Location3D = {x: 0, y: 0, z: 0, xy: "00"}
-//-- never
-let example: never;
-// ----
-type Square1 = {
-    kind: 'square',
-    size: number,
-  };
-  type Rectangle1 = {
-    kind: 'rectangle',
-    width: number,
-    height: number,
-  };
-  type Circle1 = {
-    kind: 'circle',
-    radius: number,
-  };
-  type Shape1 =
-    | Square1
-    | Rectangle1
-    | Circle1;
-  function area(s: Shape1) {
-    if (s.kind === 'square') {
-      return s.size * s.size;
-    } else if (s.kind === 'rectangle') {
-      return s.width * s.height;
-    } else if (s.kind === 'circle') {
-      return Math.PI * (s.radius ** 2);
-    }
-    const _ensureAllCasesAreHandled: never = s;  // this is an assert. It will raise a TS error if we do not handle a type
-    return _ensureAllCasesAreHandled;
-  }
-</code>

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