CODEWITHSUNDEEP
node.jstypescript
kyanro
kyanro

Reputation: 773

How to cast callback 'Function' type?

I'm using 'http' node module in typescript.

I know, if response.setEncoding then call response.on, I got callback with 'string'. so I try to cast 'string'. But I got error TS2352: Neither type 'Function' nor type 'string' is assignable to the other.

like this

import * as http from "http";
import {IncomingMessage} from "http";

http.get("http://example.com", (response: IncomingMessage) => {
    response.setEncoding("utf8");
    response.on("data", (listener: Function) => {
        if (typeof listener === "string") {
            let matchArray: RegExpMatchArray = (listener as string).match(/a/g); // TS2352: Neither type 'Function' nor type 'string' is assignable to the other.
            console.log(matchArray);
        }
    });
});

How to cast listener to string or proper way to get string?

Upvotes: 0

Views: 719

Answers (1)

Paleo
Paleo

Reputation: 23712

If the parameter listener can be a Function or a string, then it could be declared with an union type Function|string:

import * as http from "http";
import {IncomingMessage} from "http";

http.get("http://example.com", (response: IncomingMessage) => {
    response.setEncoding("utf8");
    response.on("data", (listener: Function|string) => {
        if (typeof listener === "string") {
            let matchArray: RegExpMatchArray = listener.match(/a/g);
            console.log(matchArray);
        }
    });
});

Upvotes: 1

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