Express.js error handling function for async functions - node.js

Question

How do I make express.js handle ERR_UNHANDLED_REJECTION in async route handlers? For example, how do I make it so that the code below doesn't crash on request:
import express, {NextFunction, Request, Response} from "express";
async function fails() {
throw `Test`;
}
const app = express();
app.get('/', async () => {
await fails();
});
app.use((err: any, req: Request, res: Response, next: NextFunction) => {
console.log(`err`, err);
res.send({err})
});
app.listen(9999);

Answer 1

Try Koa as it's already async.
Otherwise, create a generic wrapper function that can turn an async function into the required express response.
import express, {NextFunction, Request, Response} from "express";
function genHandler(responseHandler: Function) {
return async function theHandler(req: Request, res: Response, next: NextFunction) {
try {
const res = await responseHandler(req, res, next)
res.send(res)
}
catch (error) {
next(error)
}
}
}
async function ok() {
return 'ok'
}
async function fails() {
throw `Test`;
}
const app = express();
app.get('/', genHandler(fails));
app.get('/ok', genHandler(ok));
app.use((err: any, req: Request, res: Response, next: NextFunction) => {
console.log(`err`, err);
res.send({err})
});
app.listen(9999);
The handler generator can hide a lot of repeated async request/response complexity, like express middleware does for the non async world.

Answer 2

You can use try-catch in you route.
import express, {
NextFunction,
Request,
Response
} from "express";
async function fails() {
throw `Test`;
}
const app = express();
app.get('/', async() => {
try {
await fails();
} catch (error) {
// You catch the error in here
}
});
app.use((err: any, req: Request, res: Response, next: NextFunction) => {
console.log(`err`, err);
res.send({
err
})
});
app.listen(9999);

Answer 3

you must use try and catch block.
import express, {NextFunction, Request, Response} from "express";
async function fails() {
throw `Test`;
}
const app = express();
app.get('/', async (req, res, next){
try{
await fails();
}
catch(err){
//you can also create a global function to handle errors
return res.send(err)
}
});
app.use((err: any, req: Request, res: Response, next: NextFunction) => {
console.log(`err`, err);
res.send({err})
});
app.listen(9999);