Types of Types

• Dynamic/loose typing
• Static/strict typing

let string = 'a string'; // valid
string = true; // yup, valid
string = 0; // still valid
string = {}; // you guessed it...

Primitive Types

• null
• undefined
• Boolean
• Number
• String
• Symbol (ES6+)

Function

const foo = function() { 
  console.log('bar'); 
};

typeof foo
"function"

Object

typeof {}
"object"
typeof []
"object"
typeof new Map()
"object"

Enter TypeScript

• Superset language
• Pre-runtime enforcement
• Compiles to JS
• Enforce as much or as little as you like

Features

• Static/inference typing
• Custom types
• Intersection/union types
• Interfaces
• Enums
• Generics (<T>)
• OO features
  • public/protected/private
  • abstract classes

Let's Play!