Introduction

These examples are ordered in approximately increasing order of complexity.

• Global Functions
• Overloaded Function
• Reusable Types (Type Aliases)
• Classes

The Examples

Documentation

Code

Declaration

Use declare var to declare variables.If the variable is read-only, you can use declare const.You can also use declare let if the variable is block-scoped.

/** The number of widgets present */
declare var foo: number;

Global Functions

Documentation

You can call the function greet with a string to show a greeting to the user.

Code

greet("hello, world");

Declaration

Use declare function to declare functions.

declare function greet(greeting: string): void;

Documentation

Code

let result = myLib.makeGreeting("hello, world");
console.log("The computed greeting is:" + result);

Use declare namespace to describe types or values accessed by dotted notation.

Overloaded Functions

Documentation

The getWidget function accepts a number and returns a Widget, or accepts a string and returns a Widget array.

Code

let x: Widget = getWidget(43);
let arr: Widget[] = getWidget("all of them");

Declaration

declare function getWidget(n: number): Widget;
declare function getWidget(s: string): Widget[];

Documentation

When specifying a greeting, you must pass a GreetingSettings object.This object has the following properties:

1 - greeting: Mandatory string

2 - duration: Optional length of time (in milliseconds)

3 - color: Optional string, e.g. ‘#ff00ff’

Code

greet({
  duration: 4000
});

Declaration

Use an interface to define a type with properties.

interface GreetingSettings {
  greeting: string;
  duration?: number;
  color?: string;
}
declare function greet(setting: GreetingSettings): void;

Reusable Types (Type Aliases)

Documentation

Code

Declaration

You can use a type alias to make a shorthand for a type:

type GreetingLike = string | (() => string) | Greeter;
declare function greet(g: GreetingLike): void;

Documentation

The greeter object can log to a file or display an alert.You can provide LogOptions to .log(…) and alert options to .alert(…)

Code

const g = new Greeter("Hello");
g.log({ verbose: true });
g.alert({ modal: false, title: "Current Greeting" });

Declaration

Use namespaces to organize types.

declare namespace GreetingLib {
    interface LogOptions {
    interface AlertOptions {
        modal: boolean;
        title?: string;
        color?: string;
    }
}

You can also create nested namespaces in one declaration:

declare namespace GreetingLib.Options {
    // Refer to via GreetingLib.Options.Log
    interface Log {
        verbose?: boolean;
    }
    interface Alert {
        modal: boolean;
        title?: string;
        color?: string;
    }
}

Classes

Documentation

Code

Declaration

Use declare class to describe a class or class-like object.Classes can have properties and methods as well as a constructor.

declare class Greeter {
    constructor(greeting: string);
    greeting: string;
    showGreeting(): void;
}