Category Archives: ESLint

Fix “ESLint: Unsafe call of an `any` typed value” using express (expressJS) and TypeScript

When trying to be diligent about keeping strict types via ESLint in a TypeScript based ExpressJS, You may hit the dreaded, “ESLint: Unsafe call of an any typed value. (@typescript-eslint/no-unsafe-call)” while trying to use the default express() method via:

import express from 'express';

const app = express();

After an npm i -D @types/express the error will remain. After searching around and seeing so many fixes for importing Request and Response types, I finally found an explanation of how to fix the any typed value error on the express() method via smichel17’s response to, “express() function and express namespace ambiguity #37920”. The nuance is in that “import” returns plain objects and “require” returns returns objects and functions. Note that you cannot destructure the “require” call so to get your “Request” and “Response” types without using “express.Request” and “express.Response” you still need the traditional import statement as well.

Update your code to the following and resolve the “Unsafe call of an any typed value” error without using the dreaded escape hatch of "noImplicitAny": false.

import express = require('express');
import { Request, Response } from 'express';

const app = express();
const port = 3000;

app.get('/', (req: Request, res: Response) => {
    'Express + TypeScript Server ' +
    'With Strict Types by Joe');

app.listen(port, () => {
    `⚡️[server]: Server is running ' + 
    ' at http://localhost:${port}`);