What is the best way to apply TypeScript's interface to a function?

Question

What is the best way to apply TypeScript's interface to a function?

Looking to define an interface with function overloads and implement it?

You could start like this:

export interface ServerRouteHandler
{
  ( options: any, handlers: RequestHandler );
  ( options: any, handlers: RequestHandler[] );
  ( options: any, ...handlers: RequestHandler[] );
  ( options: any, handlers: RequestCtxHandler );
  ( options: any, handlers: RequestCtxHandler[] );
  ( options: any, ...handlers: RequestCtxHandler[] );
}

Then proceed with:

get:ServerRouteHandler = ( options: any, ...handlers: any[] ) =>
{
  return this.generateRoutes('GET', options, handlers);
}

post:ServerRouteHandler = ( options: any, ...handlers: any[] ) =>
{
  return this.generateRoutes('POST', options, handlers);
}

delete:ServerRouteHandler = ( options: any, ...handlers: any[] ) =>
{
  return this.generateRoutes('DELETE', options, handlers);
}

This approach may seem like a workaround and can slightly alter the function's behavior.

But is there another syntax available? Maybe something like:

get<ServerRouteHandler>( options: any, ...handlers: any[] )
{
  return this.generateRoutes('GET', options, handlers);
}
// Unfortunately, this does not work as expected

typescript overloading

Answer 1

Answer №1

One way to approach this situation is by defining the methods get, post, and del within a class. This allows them to be treated as functions that can be called when needed. However, a potential issue arises with the ambiguity of the type of this within these functions, making it challenging to access appropriately. By specifying the type of this as the first argument in each function, TypeScript can better understand how to handle it without adding an extra parameter. Consider the following example:

// For the sake of compilation, assume these types are strings
type RequestHandler = string;
type RequestCtxHandler = string;

interface ServerRouteHandler {
  (opts: any, handlers: RequestHandler );
  (opts: any, handlers: RequestHandler[] );
  (opts: any, ...handlers: RequestHandler[] );
  (opts: any, handlers: RequestCtxHandler );
  (opts: any, handlers: RequestCtxHandler[] );
  (opts: any, ...handlers: RequestCtxHandler[] );
}

// Example class demonstrating methods that conform to ServerRouteHandler
class Something {
    constructor(public x: number) { }

    get: ServerRouteHandler = function get(this: Something, opts: any, ...handlers: any[]) {
        console.log("get", this.x, opts, handlers);
    }
}

const something = new Something(999);
something.get({}, ["1"]);

When you execute this code snippet, the output will be get 999 Object Array[1] in the console.

As of now, there doesn't seem to be a more direct syntax available for handling this scenario.

Answer 2

One way to approach this situation is by defining the methods get, post, and del within a class. This allows them to be treated as functions that can be called when needed. However, a potential issue arises with the ambiguity of the type of this within these functions, making it challenging to access appropriately. By specifying the type of this as the first argument in each function, TypeScript can better understand how to handle it without adding an extra parameter. Consider the following example:

// For the sake of compilation, assume these types are strings
type RequestHandler = string;
type RequestCtxHandler = string;

interface ServerRouteHandler {
  (opts: any, handlers: RequestHandler );
  (opts: any, handlers: RequestHandler[] );
  (opts: any, ...handlers: RequestHandler[] );
  (opts: any, handlers: RequestCtxHandler );
  (opts: any, handlers: RequestCtxHandler[] );
  (opts: any, ...handlers: RequestCtxHandler[] );
}

// Example class demonstrating methods that conform to ServerRouteHandler
class Something {
    constructor(public x: number) { }

    get: ServerRouteHandler = function get(this: Something, opts: any, ...handlers: any[]) {
        console.log("get", this.x, opts, handlers);
    }
}

const something = new Something(999);
something.get({}, ["1"]);

When you execute this code snippet, the output will be get 999 Object Array[1] in the console.

As of now, there doesn't seem to be a more direct syntax available for handling this scenario.

What is the best way to apply TypeScript's interface to a function?

Answer №1

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