Does TypeScript allow type aliases?

Question

So I wish I could use an alias to an ugly type that looks like this:

Maybe, Problem>>[]

Something

Answer 1

A poor man's solution is to declare a dummy variable (e.g. t) with the desired type and use typeof t instead of the long type expression:

var t: { (x: number, f: { (foo: string, bar:boolean): void }): void };

var f: typeof t;
var g: typeof t;

Answer 2

From version 1.4 Typescript supports type aliases (source).

Type Aliases

You can now define an alias for a type using the type keyword:

type PrimitiveArray = Array<string|number|boolean>;
type MyNumber = number;
type NgScope = ng.IScope;
type Callback = () => void;

Type aliases are exactly the same as their original types; they are simply alternative names.

And from version 1.6 Typescript supports generic type aliases (source).

Generic type aliases

Leading up to TypeScript 1.6, type aliases were restricted to being simple aliases that shortened long type names. Unfortunately, without being able to make these generic, they had limited use. We now allow type aliases to be generic, giving them full expressive capability.

type switcharoo<T, U> = (u: U, t:T)=>T;
var f: switcharoo<number, string>;
f("bob", 4);

Answer 3

TypeScript supports imports, e.g.:

module A {
    export class c {
        d: any;
     }
}

module B {
    import moduleA = A;

    var e: moduleA.c = new moduleA.c();
}

module B2 {
    import Ac = A.c;

    var e: Ac = new Ac();
}

Update 1

Since TS 1.4 we can use type declarations:

type MyHandler = (myArgument: string) => void;

var handler: MyHandler;

Since TS 1.6 we can use local type declarations:

function f() {
    if (true) {
        interface T { x: number }
        let v: T;
        v.x = 5;
    }
    else {
        interface T { x: string }
        let v: T;
        v.x = "hello";
    }
}