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 it works…
Variables—either standalone or as arguments to a function—are decorated using a colon and then the type. For example, the first function, greeter, takes a single argument, person, which must be a string. The second function, circumference...