type interface

接口和类型别名都可以用来描述对象的形状或函数签名：

  1. interface Point {
  2.     x: number;
  3.     y: number;
  4. }
  6. interface setPoint {
  7.     (x: number, y: number): void
  8. }
  10. type tPoint = {
  11.     x: number,
  12.     y: number
  13. }
  15. type tSetPoint = (x: number, y: number) => void

与接口类型不一样，类型别名可以用于一些其他类型，比如原始类型、联合类型和元组

  1. // primitive
  2. type Name = string;
  4. // object
  5. type PartialPointX = { x: number; };
  6. type PartialPointY = { y: number; };
  8. // union
  9. type PartialPoint = PartialPointX | PartialPointY;
  11. // tuple
  12. type Data = [number, string];

接口和类型别名都能够被扩展，但语法有所不同。此外，接口和类型别名不是互斥的。接口可以扩展类型别名，而反过来是不行的。

  1. interface PartialPointX { x: number; }
  2. interface Point extends PartialPointX { 
  3.   y: number; 
  4. }
  1. type PartialPointX = { x: number; };
  2. type Point = PartialPointX & { y: number; };
  1. type PartialPointX = { x: number; };
  2. interface Point extends PartialPointX { y: number; }
  1. interface PartialPointX { x: number; }
  2. type Point = PartialPointX & { y: number; };

类可以以相同的方式实现接口或类型别名，但类不能实现使用类型别名定义的联合类型：

  1. interface Point {
  2.     x: number;
  3.     y: number;
  4. }
  6. class SomePoint implements Point {
  7.     x = 1;
  8.     y = 2;
  9. }
  11. type Point2 = {
  12.     x: number;
  13.     y: number;
  14. };
  16. class SomePoint2 implements Point2 {
  17.     x = 1;
  18.     y = 2;
  19. }
  21. type PartialPoint = { x: number; } | { y: number; };
  23. // A class can only implement an object type or 
  24. // intersection of object types with statically known members.
  25. class SomePartialPoint implements PartialPoint { // Error
  26.     x = 1;
  27.     y = 2;
  28. }

与类型别名不同，接口可以定义多次，会被自动合并为单个接口。

  1. interface Point { x: number; }
  2. interface Point { y: number; }
  4. const point: Point = { x: 1, y: 2 };