learnxinyminutes-docs/th-th/typescript.th.html.markdown

language	contributors	filename	lang
TypeScript	Philippe Vlérick https://github.com/pvlerick Worajedt Sitthidumrong https://bitbucket.org/wrj	learntypescript.ts	th-th

TypeScript เป็นภาษาที่มีเป้าหมายเพื่อทำให้การพัฒนาซอฟต์แวร์ขนาดใหญ่ด้วย JavaScript ทำได้ง่ายขึ้น โดยที่ TypeScript ได้เพิ่มแนวคิดที่พบทั่วไป อาทิ classes, modules, interfaces, generics และ static typing (ไม่บังคับ) เข้าไปในภาษา JavaScript ดังนั้น TypeScript ก็เลยเป็น Super Set ของ JavaScript อีกที โค้ด JavaScript ทุกส่วน ก็คือโค้ดที่ทำงานได้ถูกต้องใน TypeScript ทำให้เราเพิ่ม TypeScript เข้าไปใช้ในโปรเจคการพัฒนาของเราได้ไม่ยากเลย เพราะ TypeScript คอมไพล์ผลลัพธ์ออกมาเป็น JavaScript ในท้ายสุดอยู่ดี

บทความนี้จะเน้นเฉพาะ syntax ส่วนขยายของ TypeScript ซึ่งจะไม่รวมกับที่มีใน JavaScript.

การทดสอบเขียน TypeScript เริ่มได้ง่าย ๆ โดยเข้าไปที่ [Playground] (http://www.typescriptlang.org/Playground) ซึ่งคุณจะเขียนโค้ดพร้อม autocomplete และเห็นเลยว่ามันจะแปลงมาเป็นผลลัพธ์แบบ JavaScript อย่างไร

// There are 3 basic types in TypeScript
let isDone: boolean = false;
let lines: number = 42;
let name: string = "Anders";

// But you can omit the type annotation if the variables are derived
// from explicit literals
let isDone = false;
let lines = 42;
let name = "Anders";

// When it's impossible to know, there is the "Any" type
let notSure: any = 4;
notSure = "maybe a string instead";
notSure = false; // okay, definitely a boolean

// Use const keyword for constants
const numLivesForCat = 9;
numLivesForCat = 1; // Error

// For collections, there are typed arrays and generic arrays
let list: number[] = [1, 2, 3];
// Alternatively, using the generic array type
let list: Array<number> = [1, 2, 3];

// For enumerations:
enum Color { Red, Green, Blue };
let c: Color = Color.Green;

// Lastly, "void" is used in the special case of a function returning nothing
function bigHorribleAlert(): void {
  alert("I'm a little annoying box!");
}

// Functions are first class citizens, support the lambda "fat arrow" syntax and
// use type inference

// The following are equivalent, the same signature will be inferred by the
// compiler, and same JavaScript will be emitted
let f1 = function (i: number): number { return i * i; }
// Return type inferred
let f2 = function (i: number) { return i * i; }
// "Fat arrow" syntax
let f3 = (i: number): number => { return i * i; }
// "Fat arrow" syntax with return type inferred
let f4 = (i: number) => { return i * i; }
// "Fat arrow" syntax with return type inferred, braceless means no return
// keyword needed
let f5 = (i: number) => i * i;

// Interfaces are structural, anything that has the properties is compliant with
// the interface
interface Person {
  name: string;
  // Optional properties, marked with a "?"
  age?: number;
  // And of course functions
  move(): void;
}

// Object that implements the "Person" interface
// Can be treated as a Person since it has the name and move properties
let p: Person = { name: "Bobby", move: () => { } };
// Objects that have the optional property:
let validPerson: Person = { name: "Bobby", age: 42, move: () => { } };
// Is not a person because age is not a number
let invalidPerson: Person = { name: "Bobby", age: true };

// Interfaces can also describe a function type
interface SearchFunc {
  (source: string, subString: string): boolean;
}
// Only the parameters' types are important, names are not important.
let mySearch: SearchFunc;
mySearch = function (src: string, sub: string) {
  return src.search(sub) != -1;
}

// Classes - members are public by default
class Point {
  // Properties
  x: number;

  // Constructor - the public/private keywords in this context will generate
  // the boiler plate code for the property and the initialization in the
  // constructor.
  // In this example, "y" will be defined just like "x" is, but with less code
  // Default values are also supported

  constructor(x: number, public y: number = 0) {
    this.x = x;
  }

  // Functions
  dist() { return Math.sqrt(this.x * this.x + this.y * this.y); }

  // Static members
  static origin = new Point(0, 0);
}

// Classes can be explicitly marked as implementing an interface.
// Any missing properties will then cause an error at compile-time.
class PointPerson implements Person {
    name: string
    move() {}
}

let p1 = new Point(10, 20);
let p2 = new Point(25); //y will be 0

// Inheritance
class Point3D extends Point {
  constructor(x: number, y: number, public z: number = 0) {
    super(x, y); // Explicit call to the super class constructor is mandatory
  }

  // Overwrite
  dist() {
    let d = super.dist();
    return Math.sqrt(d * d + this.z * this.z);
  }
}

// Modules, "." can be used as separator for sub modules
module Geometry {
  export class Square {
    constructor(public sideLength: number = 0) {
    }
    area() {
      return Math.pow(this.sideLength, 2);
    }
  }
}

let s1 = new Geometry.Square(5);

// Local alias for referencing a module
import G = Geometry;

let s2 = new G.Square(10);

// Generics
// Classes
class Tuple<T1, T2> {
  constructor(public item1: T1, public item2: T2) {
  }
}

// Interfaces
interface Pair<T> {
  item1: T;
  item2: T;
}

// And functions
let pairToTuple = function <T>(p: Pair<T>) {
  return new Tuple(p.item1, p.item2);
};

let tuple = pairToTuple({ item1: "hello", item2: "world" });

// Including references to a definition file:
/// <reference path="jquery.d.ts" />

// Template Strings (strings that use backticks)
// String Interpolation with Template Strings
let name = 'Tyrone';
let greeting = `Hi ${name}, how are you?`
// Multiline Strings with Template Strings
let multiline = `This is an example
of a multiline string`;

// READONLY: New Feature in TypeScript 3.1
interface Person {
  readonly name: string;
  readonly age: number;
}

var p1: Person = { name: "Tyrone", age: 42 };
p1.age = 25; // Error, p1.x is read-only

var p2 = { name: "John", age: 60 };
var p3: Person = p2; // Ok, read-only alias for p2
p3.x = 35; // Error, p3.x is read-only
p2.x = 45; // Ok, but also changes p3.x because of aliasing

class Car {
  readonly make: string;
  readonly model: string;
  readonly year = 2018;

  constructor() {
    this.make = "Unknown Make"; // Assignment permitted in constructor
    this.model = "Unknown Model"; // Assignment permitted in constructor
  }
}

let numbers: Array<number> = [0, 1, 2, 3, 4];
let moreNumbers: ReadonlyArray<number> = numbers;
moreNumbers[5] = 5; // Error, elements are read-only
moreNumbers.push(5); // Error, no push method (because it mutates array)
moreNumbers.length = 3; // Error, length is read-only
numbers = moreNumbers; // Error, mutating methods are missing

อ่านเพิ่มเติมที่

• [TypeScript Official website] (http://www.typescriptlang.org/)
• [TypeScript language specifications] (https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md)
• [Anders Hejlsberg - Introducing TypeScript on Channel 9] (http://channel9.msdn.com/posts/Anders-Hejlsberg-Introducing-TypeScript)
• [Source Code on GitHub] (https://github.com/Microsoft/TypeScript)
• [Definitely Typed - repository for type definitions] (http://definitelytyped.org/)