CODEWITHSUNDEEP
javascripttypescripttypescript-typings
Vivek Santhosh
Vivek Santhosh

Reputation: 299

How can i apply an interface to an anonymous callback function in typescript

I have an interface that looks like this

interface CallBackHandler{
 (err: Error, response: {statusCode: number, body: object}):void
}

and i want to apply that interface to the callback of this 

    request({
    url: url,
    method: "GET",
    withCredentials: false,
    json: true,
    headers: headers
  }, (err, response) => {
    this.handleResponse(err, response, resolve, reject);
  });

but im getting a error saying the function must return something if the return type is not void when i add the interface 

(err, response): CallBackHandler => {
    this.handleResponse(err, response, resolve, reject);
  }

what is the correct way to apply this interface?

Upvotes: 4

Views: 289

Answers (2)

rossipedia
rossipedia

Reputation: 59397

If request() already has the type signature:

function request(options, callback: CallBackHandler) {
   ...
}

Then you shouldn't need to do anything, as the callback you provide will be type-checked accordingly.

If that function doesn't already have that type signature, and you want to manually cast your callback to CallBackHandler, then you will need to wrap the callback function in parentheses and cast that expression, like so:

request({
    ...etc
}, ((err, response) => {
    this.handleResponse(err, response, resolve, reject);
}) as CallBackHandler);

Upvotes: 1

riyaz-ali
riyaz-ali

Reputation: 9102

You can have something like

request({
  url: url,
  method: "GET",
  withCredentials: false,
  json: true,
  headers: headers
}, (err: Error, response: {statusCode: number, body: object}) => {
  this.handleResponse(err, response, resolve, reject);
});

Upvotes: 0

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