Interfaces in place of type aliases

Define a simple interface for structures

interface Dimensions {
  width: number,
  height: number
}

Can be used similarly to types

let dimensions: Dimensions = {
  width: 200,
  height: 100
}

Interfaces for objects

Define an interface for an object with methods

interface Drawable {
  draw(): void,
  dimensions: Dimensions,
}

Implement such an interface using classes

class Painting implements Drawable {
  // short form for field initializers
  constructor(private dimensions: Dimensions) {
  }

  draw() {
    console.log('drawing ' + this.dimensions.width + 'x' + this.dimensions.height);
  }
}

Instantiate an object

let monaLisa = new Painting({width: 100, height: 200})
monaLisa.draw()

Function types

type Procedure = (arg: number) => void

let push: Procedure = (arg: number) => {
  ...
}

Type aliases for special cases

type AnyRecord = Record<string, any>;

Generic dictionaries

type Dictionary<T> = Record<string, T>;

let m: Dictionary<number> = {"two": 2, "three": 3}