了不起的 TypeScript 入门教程 [1.2 w 字]

$ npm install -g typescript

$ tsc helloworld.ts
# helloworld.ts => helloworld.js

let isDone: boolean = false;
// ES5：var isDone = false;

let count: number = 10;
// ES5：var count = 10;

let name: string = "Semliker";
// ES5：var name = 'Semlinker';

let list: number[] = [1, 2, 3];
// ES5：var list = [1,2,3];
let list: Array<number> = [1, 2, 3]; // Array<number>泛型语法
// ES5：var list = [1,2,3];

enum Direction {
  NORTH,
  SOUTH,
  EAST,
  WEST,
}
let dir: Direction = Direction.NORTH;

"use strict";
var Direction;
(function (Direction) {
  Direction[(Direction["NORTH"] = 0)] = "NORTH";
  Direction[(Direction["SOUTH"] = 1)] = "SOUTH";
  Direction[(Direction["EAST"] = 2)] = "EAST";
  Direction[(Direction["WEST"] = 3)] = "WEST";
})(Direction || (Direction = {}));
var dir = Direction.NORTH;

enum Direction {
  NORTH = 3,
  SOUTH,
  EAST,
  WEST,
}

enum Direction {
  NORTH = "NORTH",
  SOUTH = "SOUTH",
  EAST = "EAST",
  WEST = "WEST",
}

"use strict";
var Direction;
(function (Direction) {
    Direction["NORTH"] = "NORTH";
    Direction["SOUTH"] = "SOUTH";
    Direction["EAST"] = "EAST";
    Direction["WEST"] = "WEST";
})(Direction || (Direction = {}));

enum Enum {
  A,
  B,
  C = "C",
  D = "D",
  E = 8,
  F,
}

"use strict";
var Enum;
(function (Enum) {
    Enum[Enum["A"] = 0] = "A";
    Enum[Enum["B"] = 1] = "B";
    Enum["C"] = "C";
    Enum["D"] = "D";
    Enum[Enum["E"] = 8] = "E";
    Enum[Enum["F"] = 9] = "F";
})(Enum || (Enum = {}));

console.log(Enum.A) //输出：0
console.log(Enum[0]) // 输出：A

let notSure: any = 666;
notSure = "Semlinker";
notSure = false;

let value: any;
value.foo.bar; // OK
value.trim(); // OK
value(); // OK
new value(); // OK
value[0][1]; // OK

let value: unknown;
value = true; // OK
value = 42; // OK
value = "Hello World"; // OK
value = []; // OK
value = {}; // OK
value = Math.random; // OK
value = null; // OK
value = undefined; // OK
value = new TypeError(); // OK
value = Symbol("type"); // OK

let value: unknown;
let value1: unknown = value; // OK
let value2: any = value; // OK
let value3: boolean = value; // Error
let value4: number = value; // Error
let value5: string = value; // Error
let value6: object = value; // Error
let value7: any[] = value; // Error
let value8: Function = value; // Error

let value: unknown;
value.foo.bar; // Error
value.trim(); // Error
value(); // Error
new value(); // Error
value[0][1]; // Error

let tupleType: [string, boolean];
tupleType = ["Semlinker", true];

console.log(tupleType[0]); // Semlinker
console.log(tupleType[1]); // true

tupleType = [true, "Semlinker"];

[0]: Type 'true' is not assignable to type 'string'.
[1]: Type 'string' is not assignable to type 'boolean'.

tupleType = ["Semlinker"];

Property '1' is missing in type '[string]' but required in type '[string, boolean]'.

// 声明函数返回值为void
function warnUser(): void {
  console.log("This is my warning message");
}

"use strict";
function warnUser() {
  console.log("This is my warning message");
}

let unusable: void = undefined;

let u: undefined = undefined;
let n: null = null;

// 返回never的函数必须存在无法达到的终点
function error(message: string): never {
  throw new Error(message);
}
function infiniteLoop(): never {
  while (true) {}
}

type Foo = string | number;
function controlFlowAnalysisWithNever(foo: Foo) {
  if (typeof foo === "string") {
    // 这里 foo 被收窄为 string 类型
  } else if (typeof foo === "number") {
    // 这里 foo 被收窄为 number 类型
  } else {
    // foo 在这里是 never
    const check: never = foo;
  }
}

type Foo = string | number | boolean;

let someValue: any = "this is a string";
let strLength: number = (<string>someValue).length;

let someValue: any = "this is a string";
let strLength: number = (someValue as string).length;

interface Admin {
  name: string;
  privileges: string[];
}
interface Employee {
  name: string;
  startDate: Date;
}
type UnknownEmployee = Employee | Admin;
function printEmployeeInformation(emp: UnknownEmployee) {
  console.log("Name: " + emp.name);
  if ("privileges" in emp) {
    console.log("Privileges: " + emp.privileges);
  }
  if ("startDate" in emp) {
    console.log("Start Date: " + emp.startDate);
  }
}

function padLeft(value: string, padding: string | number) {
  if (typeof padding === "number") {
      return Array(padding + 1).join(" ") + value;
  }
  if (typeof padding === "string") {
      return padding + value;
  }
  throw new Error(`Expected string or number, got '${padding}'.`);
}

interface Padder {
  getPaddingString(): string;
}
class SpaceRepeatingPadder implements Padder {
  constructor(private numSpaces: number) {}
  getPaddingString() {
    return Array(this.numSpaces + 1).join(" ");
  }
}
class StringPadder implements Padder {
  constructor(private value: string) {}
  getPaddingString() {
    return this.value;
  }
}
let padder: Padder = new SpaceRepeatingPadder(6);
if (padder instanceof SpaceRepeatingPadder) {
  // padder的类型收窄为 'SpaceRepeatingPadder'
}

function isNumber(x: any): x is number {
  return typeof x === "number";
}
function isString(x: any): x is string {
  return typeof x === "string";
}

const sayHello = (name: string | undefined) => {
  /* ... */
};

sayHello("Semlinker");
sayHello(undefined);

enum CarTransmission {
  Automatic = 200,
  Manual = 300
}
interface Motorcycle {
  vType: "motorcycle"; // discriminant
  make: number; // year
}
interface Car {
  vType: "car"; // discriminant
  transmission: CarTransmission
}
interface Truck {
  vType: "truck"; // discriminant
  capacity: number; // in tons
}

type Vehicle = Motorcycle | Car | Truck;

const EVALUATION_FACTOR = Math.PI; 
function evaluatePrice(vehicle: Vehicle) {
  return vehicle.capacity * EVALUATION_FACTOR;
}
const myTruck: Truck = { vType: "truck", capacity: 9.5 };
evaluatePrice(myTruck);

Property 'capacity' does not exist on type 'Vehicle'.
Property 'capacity' does not exist on type 'Motorcycle'.

function evaluatePrice(vehicle: Vehicle) {
  switch(vehicle.vType) {
    case "car":
      return vehicle.transmission * EVALUATION_FACTOR;
    case "truck":
      return vehicle.capacity * EVALUATION_FACTOR;
    case "motorcycle":
      return vehicle.make * EVALUATION_FACTOR;
  }
}

type Message = string | string[];
let greet = (message: Message) => {
  // ...
};

interface IPerson {
  id: string;
  age: number;
}
interface IWorker {
  companyId: string;
}
type IStaff = IPerson & IWorker;
const staff: IStaff = {
  id: 'E1006',
  age: 33,
  companyId: 'EFT'
};
console.dir(staff)

myBooks.forEach(() => console.log('reading'));
myBooks.forEach(title => console.log(title));
myBooks.forEach((title, idx, arr) =>
  console.log(idx + '-' + title);
);
myBooks.forEach((title, idx, arr) => {
  console.log(idx + '-' + title);
});

// 未使用箭头函数
function Book() {
  let self = this;
  self.publishDate = 2016;
  setInterval(function () {
    console.log(self.publishDate);
  }, 1000);
}
// 使用箭头函数
function Book() {
  this.publishDate = 2016;
  setInterval(() => {
    console.log(this.publishDate);
  }, 1000);
}

function createUserId(name: string, id: number): string {
  return name + id;
}

let IdGenerator: (chars: string, nums: number) => string;
function createUserId(name: string, id: number): string {
  return name + id;
}
IdGenerator = createUserId;

// 可选参数
function createUserId(name: string, id: number, age?: number): string {
  return name + id;
}
// 默认参数
function createUserId(
  name: string = "Semlinker",
  id: number,
  age?: number
): string {
  return name + id;
}

function push(array, ...items) {
  items.forEach(function (item) {
    array.push(item);
  });
}
let a = [];
push(a, 1, 2, 3);

function add(a: number, b: number): number;
function add(a: string, b: string): string;
function add(a: string, b: number): string;
function add(a: number, b: string): string;
function add(a: Combinable, b: Combinable) {
  if (typeof a === "string" || typeof b === "string") {
    return a.toString() + b.toString();
  }
  return a + b;
}

class Calculator {
  add(a: number, b: number): number;
  add(a: string, b: string): string;
  add(a: string, b: number): string;
  add(a: number, b: string): string;
  add(a: Combinable, b: Combinable) {
    if (typeof a === "string" || typeof b === "string") {
      return a.toString() + b.toString();
    }
    return a + b;
  }
}
const calculator = new Calculator();
const result = calculator.add("Semlinker", " Kakuqo");

let x: number; let y: number; let z: number;
let five_array = [0,1,2,3,4];
[x,y,z] = five_array;

let two_array = [0, 1];
let five_array = [...two_array, 2, 3, 4];