The JavaScript JSON Cookbook

How to annotate simple types using TypeScript

Type annotations with TypeScript are simple decorators appended to the variable or function after a colon. There's support for the same primitive types as in JavaScript, and to declare interfaces and classes, which we will discuss next.

How to do it…

Here's a simple example of some variable declarations and two function declarations:

function greeter(person: string): string {
  return "Hello, " + person;
}

function circumference(radius: number) : number {
  var pi: number = 3.141592654;
  return 2 * pi * radius;
}

var user: string = "Ray";

console.log(greeter(user));
console.log("You need " + 
circumference(2) + 
  " meters of fence for your dog.");

This example shows how to annotate functions and variables.

How ...