对象类型

在 JavaScript 中，我们分组和传递数据的基本方式是通过对象。在 TypeScript 中，我们通过对象类型来表示它们。

正如我们所见，它们可以是匿名的：

function greet(person: { name: string; age: number }) {
  //                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  return "Hello " + person.name;
}

或者它们可以通过使用任何一个接口来命名

interface Person {
  //      ^^^^^^
  name: string;
  age: number;
}

function greet(person: Person) {
  return "Hello " + person.name;
}

或类型别名。

type Person = {
  // ^^^^^^
  name: string;
  age: number;
};

function greet(person: Person) {
  return "Hello " + person.name;
}

在上述所有三个示例中，我们编写的函数接受包含属性 name（必须是 string）和 age（必须是 number）的对象。

属性修饰符

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可选属性

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interface Shape {}
declare function getShape(): Shape;

interface PaintOptions {
  shape: Shape;
  xPos?: number;
  //  ^
  yPos?: number;
  //  ^
}

function paintShape(opts: PaintOptions) {
  // ...
}

const shape = getShape();
paintShape({ shape });
paintShape({ shape, xPos: 100 });
paintShape({ shape, yPos: 100 });
paintShape({ shape, xPos: 100, yPos: 100 });

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interface Shape {}
declare function getShape(): Shape;

interface PaintOptions {
  shape: Shape;
  xPos?: number;
  yPos?: number;
}

function paintShape(opts: PaintOptions) {
  let xPos = opts.xPos;
  let yPos = opts.yPos;
  // ...
}

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interface Shape {}
declare function getShape(): Shape;

interface PaintOptions {
  shape: Shape;
  xPos?: number;
  yPos?: number;
}

function paintShape(opts: PaintOptions) {
  let xPos = opts.xPos === undefined ? 0 : opts.xPos;
  let yPos = opts.yPos === undefined ? 0 : opts.yPos;
  // ...
}

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interface Shape {}
declare function getShape(): Shape;

interface PaintOptions {
  shape: Shape;
  xPos?: number;
  yPos?: number;
}

function paintShape({ shape, xPos = 0, yPos = 0 }: PaintOptions) {
  console.log("x coordinate at", xPos);
  console.log("y coordinate at", yPos);
  // ...
}

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interface Shape {}
declare function render(x: unknown);
function draw({ shape: Shape, xPos: number = 100 /*...*/ }) {
  render(shape);
  render(xPos);
}

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readonly 属性

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interface SomeType {
  readonly prop: string;
}

function doSomething(obj: SomeType) {
  // We can read from 'obj.prop'.
  console.log(`prop has the value '${obj.prop}'.`);

  // But we can't re-assign it.
  obj.prop = "hello";
}

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interface Home {
  readonly resident: { name: string; age: number };
}

function visitForBirthday(home: Home) {
  // We can read and update properties from 'home.resident'.
  console.log(`Happy birthday ${home.resident.name}!`);
  home.resident.age++;
}

function evict(home: Home) {
  // But we can't write to the 'resident' property itself on a 'Home'.
  home.resident = {
    name: "Victor the Evictor",
    age: 42,
  };
}

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interface Person {
  name: string;
  age: number;
}

interface ReadonlyPerson {
  readonly name: string;
  readonly age: number;
}

let writablePerson: Person = {
  name: "Person McPersonface",
  age: 42,
};

// works
let readonlyPerson: ReadonlyPerson = writablePerson;

console.log(readonlyPerson.age); // prints '42'
writablePerson.age++;
console.log(readonlyPerson.age); // prints '43'

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索引签名

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declare function getStringArray(): StringArray;
interface StringArray {
  [index: number]: string;
}

const myArray: StringArray = getStringArray();
const secondItem = myArray[1];

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interface NumberDictionary {
  [index: string]: number;

  length: number; // ok
  name: string;
}

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interface NumberOrStringDictionary {
  [index: string]: number | string;
  length: number; // ok, length is a number
  name: string; // ok, name is a string
}

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declare function getReadOnlyStringArray(): ReadonlyStringArray;
interface ReadonlyStringArray {
  readonly [index: number]: string;
}

let myArray: ReadonlyStringArray = getReadOnlyStringArray();
myArray[2] = "Mallory";

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扩展类型

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interface BasicAddress {
  name?: string;
  street: string;
  city: string;
  country: string;
  postalCode: string;
}

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interface AddressWithUnit {
  name?: string;
  unit: string;
//^^^^^^^^^^^^^
  street: string;
  city: string;
  country: string;
  postalCode: string;
}

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interface BasicAddress {
  name?: string;
  street: string;
  city: string;
  country: string;
  postalCode: string;
}

interface AddressWithUnit extends BasicAddress {
  unit: string;
}

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interface Colorful {
  color: string;
}

interface Circle {
  radius: number;
}

interface ColorfulCircle extends Colorful, Circle {}

const cc: ColorfulCircle = {
  color: "red",
  radius: 42,
};

交集类型

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interface Colorful {
  color: string;
}
interface Circle {
  radius: number;
}

type ColorfulCircle = Colorful & Circle;

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interface Colorful {
  color: string;
}
interface Circle {
  radius: number;
}
function draw(circle: Colorful & Circle) {
  console.log(`Color was ${circle.color}`);
  console.log(`Radius was ${circle.radius}`);
}

// okay
draw({ color: "blue", radius: 42 });

// oops
draw({ color: "red", raidus: 42 });

接口与交集

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泛型对象类型

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interface Box {
  contents: any;
}

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interface Box {
  contents: unknown;
}

let x: Box = {
  contents: "hello world",
};

// we could check 'x.contents'
if (typeof x.contents === "string") {
  console.log(x.contents.toLowerCase());
}

// or we could use a type assertion
console.log((x.contents as string).toLowerCase());

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interface NumberBox {
  contents: number;
}

interface StringBox {
  contents: string;
}

interface BooleanBox {
  contents: boolean;
}

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interface NumberBox {
  contents: number;
}

interface StringBox {
  contents: string;
}

interface BooleanBox {
  contents: boolean;
}
function setContents(box: StringBox, newContents: string): void;
function setContents(box: NumberBox, newContents: number): void;
function setContents(box: BooleanBox, newContents: boolean): void;
function setContents(box: { contents: any }, newContents: any) {
  box.contents = newContents;
}

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interface Box<Type> {
  contents: Type;
}

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interface Box<Type> {
  contents: Type;
}
let box: Box<string>;

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interface Box<Type> {
  contents: Type;
}
interface StringBox {
  contents: string;
}

let boxA: Box<string> = { contents: "hello" };
boxA.contents;

let boxB: StringBox = { contents: "world" };
boxB.contents;

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interface Box<Type> {
  contents: Type;
}

interface Apple {
  // ....
}

// Same as '{ contents: Apple }'.
type AppleBox = Box<Apple>;

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interface Box<Type> {
  contents: Type;
}

function setContents<Type>(box: Box<Type>, newContents: Type) {
  box.contents = newContents;
}

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interface Box<Type> {
  contents: Type;
}

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type Box<Type> = {
  contents: Type;
};

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type OrNull<Type> = Type | null;

type OneOrMany<Type> = Type | Type[];

type OneOrManyOrNull<Type> = OrNull<OneOrMany<Type>>;

type OneOrManyOrNullStrings = OneOrManyOrNull<string>;

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Array 类型

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function doSomething(value: Array<string>) {
  // ...
}

let myArray: string[] = ["hello", "world"];

// either of these work!
doSomething(myArray);
doSomething(new Array("hello", "world"));

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interface Number {}
interface String {}
interface Boolean {}
interface Symbol {}
interface Array<Type> {
  /**
   * Gets or sets the length of the array.
   */
  length: number;

  /**
   * Removes the last element from an array and returns it.
   */
  pop(): Type | undefined;

  /**
   * Appends new elements to an array, and returns the new length of the array.
   */
  push(...items: Type[]): number;

  // ...
}

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ReadonlyArray 类型

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function doStuff(values: ReadonlyArray<string>) {
  // We can read from 'values'...
  const copy = values.slice();
  console.log(`The first value is ${values[0]}`);

  // ...but we can't mutate 'values'.
  values.push("hello!");
}

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new ReadonlyArray("red", "green", "blue");

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const roArray: ReadonlyArray<string> = ["red", "green", "blue"];

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function doStuff(values: readonly string[]) {
  //                     ^^^^^^^^^^^^^^^^^
  // We can read from 'values'...
  const copy = values.slice();
  console.log(`The first value is ${values[0]}`);

  // ...but we can't mutate 'values'.
  values.push("hello!");
}

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let x: readonly string[] = [];
let y: string[] = [];

x = y;
y = x;

元组类型

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type StringNumberPair = [string, number];
//                      ^^^^^^^^^^^^^^^^

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function doSomething(pair: [string, number]) {
  const a = pair[0];
  const b = pair[1];
  // ...
}

doSomething(["hello", 42]);

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function doSomething(pair: [string, number]) {
  // ...

  const c = pair[2];
}

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function doSomething(stringHash: [string, number]) {
  const [inputString, hash] = stringHash;

  console.log(inputString);

  console.log(hash);
}

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interface StringNumberPair {
  // specialized properties
  length: 2;
  0: string;
  1: number;

  // Other 'Array<string | number>' members...
  slice(start?: number, end?: number): Array<string | number>;
}

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type Either2dOr3d = [number, number, number?];

function setCoordinate(coord: Either2dOr3d) {
  const [x, y, z] = coord;

  console.log(`Provided coordinates had ${coord.length} dimensions`);
}

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type StringNumberBooleans = [string, number, ...boolean[]];
type StringBooleansNumber = [string, ...boolean[], number];
type BooleansStringNumber = [...boolean[], string, number];

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type StringNumberBooleans = [string, number, ...boolean[]];
const a: StringNumberBooleans = ["hello", 1];
const b: StringNumberBooleans = ["beautiful", 2, true];
const c: StringNumberBooleans = ["world", 3, true, false, true, false, true];

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function readButtonInput(...args: [string, number, ...boolean[]]) {
  const [name, version, ...input] = args;
  // ...
}

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function readButtonInput(name: string, version: number, ...input: boolean[]) {
  // ...
}

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readonly 元组类型

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function doSomething(pair: readonly [string, number]) {
  //                       ^^^^^^^^^^^^^^^^^^^^^^^^^
  // ...
}

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function doSomething(pair: readonly [string, number]) {
  pair[0] = "hello!";
}

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let point = [3, 4] as const;

function distanceFromOrigin([x, y]: [number, number]) {
  return Math.sqrt(x ** 2 + y ** 2);
}

distanceFromOrigin(point);

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