Index signature for objects with function parameters

Question

I need some advice on a tricky syntax problem. I have a longer list of all HTTP methods and would like to call the appropriate user function.

Simplified code:

const httpMethods = {
  'connect': this.connect(req, res),
  'copy': this.copy(req, res),
  'delete': this.delete(req, res),
  'get': this.get(req, res),
  ...
}

let callFunction = httpMethods['get']
callFunction(req, res)

How can I create an index signature for the object httpMethods or type cast the callFunction to avoid TS errors?

what TS errors are you getting exactly? Can you add the error trace here? — AkshayM, Oct 29 '18 at 09:50
The error in German is:

TS 7017, "Das Element weist implizit einen Typ \"any\" auf, weil der Typ \"{ 'connect': void; 'copy': void; 'delete': void; 'get': void; 'head': void; 'link': void; 'lock': void; 'options': void; 'patch': void; 'post': void; 'pri': void; 'propfind': void; 'purge': void; 'put': void; 'trace': void; 'unlink': void; 'unlock': void; 'view': void; }\" keine Indexsignatur umfasst."
Code is as follows:
let methodFunction = httpMethods[requestData.httpMethod] methodFunction(requestData, response) — Andy Brunner, Oct 29 '18 at 10:26

Rajab Shakirov · Accepted Answer · 2018-10-29T11:05:25.263

You could cast it like this:

let key = "get";
let callFunction = (<any>httpMethods)[key];
callFunction(req, res);

or like this:

interface ISomeObject {
  connect: any;
  copy: any;
  delete: any;
  get: any;
  [key: string]: any;
}

const httpMethods: ISomeObject  = {
  'connect': this.connect(req, res),
  'copy': this.copy(req, res),
  'delete': this.delete(req, res),
  'get': this.get(req, res),
  ...
}

let key: string = "get";
let callFunction = httpMethods[key];
callFunction(req, res);

I adapted an example from this answer: https://stackoverflow.com/a/35209016/3914072

There are additional answers too.

Index signature for objects with function parameters

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