typescript named parameters like used in angularjs?

Question

I'm trying to learn both TypeScript and Angular (and thus JavaScript).

Going through the Angular tutorials, I see they do stuff like this:

In normal javascript:

function CreateCtrl($scope, $location, Project){
// do stuff
}

For full example, see the "Wire up a backend" project.js example on the Angular homepage.

The kicker is, those parameters could be in any order (or not there at all), and Project is actually a user defined variable/type. The Angular framework is able to map the parameters to actual objects.

So now to Typescript, how can I recreate this type of functionality? I would like to describe Angular's behavior in some way, to let me wrap it in Typescript (strongly type this flexible property injection).

Fenton · Accepted Answer · 2013-02-18 09:28:30Z

16

There is an AngularJS type definition on Definitely Typed that lets you use Angular from TypeScript.

If I was creating a definition for an existing function such as this (in the absence of named arguments), I would probably either define them in a specific order (even though I know they could be passed in varying orders in plain JavaScript) or create a set of function overloads that matched the possibilities I wanted to expose, like this:

interface Example {
    ($scope: bool, $location: string, Project: number): void;
    ($location: string, $scope: bool, Project: number): void;
    (Project: number, $scope: bool, $location: string): void;
}

declare var example: Example;

When I attempt to call example( I get intellisense with the three options and if I don't use one of these combinations I get a compiler warning.

In JavaScript, named arguments are normally created with an object, so if I was writing a new method that could accept arguments in this way I would do this...

interface ExampleArguments {
    scope: bool;
    location: string;
    project: number;
}

var example = function (exampleArguments: ExampleArguments) {

};

example({ scope: true, project: 4, location: 'hi' });

Which is statically typed and checked in TypeScript.

answered Feb 18, 2013 at 9:28

Fenton

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2 Comments

JasonS Over a year ago

basically it sounds like you are saying "no, you can't do it". is that right? i use angularjs d.ts and that doesn't help. also, your bottom example, angular's framework does the calling, so i don't have any control over that. maybe typescript doesn't have any way of handling this right now huh.

Fenton Over a year ago

Named arguments were proposed, but rejected from the TypeScript language specification - so it isn't possible to allow exactly as you describe - but you can formalise it so they are in a fixed order and get what you want (even though Angular would accept any order). typescript.codeplex.com/workitem/256

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