Declaration Reference

Objects with Properties

Documentation

The global variable myLib has a function makeGreeting for creating greetings, and a property numberOfGreetings indicating the number of greetings made so far.

Code

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

letcount = myLib.numberOfGreetings;

Declaration

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

declare namespace myLib {
functionmakeGreeting(s: string): string;
letnumberOfGreetings: number;
}

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);

letarr: Widget[] = getWidget("all of them");

Declaration

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

Reusable Types (Interfaces)

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({
greeting:"hello world",
duration:4000
});

Declaration

Use an interface to define a type with properties.

interface GreetingSettings {
greeting: string;
duration?: number;
color?: string;
}

declarefunctiongreet(setting: GreetingSettings): void;

Reusable Types (Type Aliases)

Documentation

Anywhere a greeting is expected, you can provide a string, a function returning a string, or a Greeter instance.

Code

function getGreeting() {
return"howdy";
}
classMyGreeterextendsGreeter {}

greet("hello");
greet(getGreeting);
greet(newMyGreeter());

Declaration

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

type GreetingLike = string | (() => string) | MyGreeter;

declarefunctiongreet(g: GreetingLike): void;

Organizing Types

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 {
interfaceLogOptions {
verbose?: boolean;
  }
interfaceAlertOptions {
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
interfaceLog {
verbose?: boolean;
  }
interfaceAlert {
modal: boolean;
title?: string;
color?: string;
  }
}

Classes

Documentation

You can create a greeter by instantiating the Greeter object, or create a customized greeter by extending from it.

Code

const myGreeter = new Greeter("hello, world");
myGreeter.greeting = "howdy";
myGreeter.showGreeting();

classSpecialGreeterextendsGreeter {
constructor() {
super("Very special greetings");
  }
}

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;
}

Global Variables

Documentation

The global variable foo contains the number of widgets present.

Code

console.log("Half the number of widgets is " + foo / 2);

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 */
declarevarfoo: 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;