#typescript interfaces vs types

interface-vs-types.ts

//extending interfaces
interface PartialPointX { x: number; }
interface Point extends PartialPointX { y: number; }

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

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

//Type alias extends interfaces
interface PartialPointX { x: number; }
type Point = PartialPointX & { y: number; };

//defining the interface for objects
interface Point {
  x: number;
  y: number;
}

//using types as well
type Point2 = {
  x: number;
  y: number;
};

//implementing the Interface
class SomePoint implements Point {
  x: 1;
  y: 2;
}

//Implementing the Type alias
class SomePoint2 implements Point2 {
  x: 1;
  y: 2;
}

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

// This is the only thing you can't do: implement a union type
class SomePartialPoint implements PartialPoint {
  x: 1;
  y: 2;
}


// The only extra feature Interfaces bring to the table (that Type aliases don’t), 
// is “declaration merging” which means you can define the same interface several 
// times and with each definition, the properties get merged:

interface Point { x: number; } //declaration #1
interface Point { y: number; } //declaration #2

// These two declarations become:
// interface Point { x: number; y: number; }
const point: Point = { x: 1, y: 2 };