interface与type

总结自：https://stackoverflow.com/questions/37233735/typescript-interfaces-vs-types

1、都能用来描述对象与函数，只是写法不同

//对象
interface Point {
  x: number;
  y: number;
}

//函数
interface SetPoint {
  (x: number, y: number): void;
}

type Point = {
  x: number;
  y: number;
};

type SetPoint = (x: number, y: number) => void;

2、type还可以用来描述原始类型、联合类型以及元组

// primitive
type Name = string;// union
type PartialPoint = PartialPointX | PartialPointY;

// tuple
type Data = [number, string];

3、都能实现继承（写法不同），且可交叉继承（interface继承type，type继承interface）

interface继承interface（extends）

interface PartialPointX { x: number; }
interface Point extends PartialPointX { y: number; }

type继承type（&）

type PartialPointX = { x: number; };
type Point = PartialPointX & { y: number; };

interface继承type （同interface继承interface）

type PartialPointX = { x: number; };
interface Point extends PartialPointX { y: number; }

type继承interface （同type继承type）

interface PartialPointX { x: number; }
type Point = PartialPointX & { y: number; };

4、类可实现interface与type，方式相同（都是implements）

class与interface都是静态的，因此当type用来描述联合类型时不能被实现

interface Point {
  x: number;
  y: number;
}

class SomePoint implements Point {
  x: 1;
  y: 2;
}

type Point2 = {
  x: number;
  y: number;
};

class SomePoint2 implements Point2 {
  x: 1;
  y: 2;
}

type PartialPoint = { x: number; } | { y: number; };

// FIXME: can not implement a union type
class SomePartialPoint implements PartialPoint {
  x: 1;
  y: 2;
}

5、interface可被定义多次，且每次定义的属性最后都能合并

// These two declarations become:
// interface Point { x: number; y: number; }
interface Point { x: number; }
interface Point { y: number; }

const point: Point = { x: 1, y: 2 };