Express make try/catch block into middleware to avoid duplication - node.js

Question

Im writing my expressJs application, and Im finding in my routes controller the same duplicated code for catching exception, I was wondering how to avoid this.
I have checked this thread, but I get this error "Cannot read property 'catch' of undefined" : Express Try and Catch in Form of middleware
this is my route.js
const express = require("express");
const createHttpError = require("http-errors");
const Validator = require("../middlewares/Validator");
const TaskNotFoundException = require("../services/TaskNotFoundException");
const TaskService = require("../services/TaskService");
router.get("/tasks", async (req, res, next) => {
try {
const data = await TaskService.getTasks();
res.send({ code: 200, message: "Success", data });
} catch (error) {
next(createHttpError(500));
}
});
router.get("/task/:id", async (req, res, next) => {
const { id } = req.params;
try {
const data = await TaskService.getTask(id);
res.send({ code: 200, message: "Success", data });
} catch (error) {
if (error instanceof TaskNotFoundException) {
next(createHttpError(404));
} else {
next(createHttpError(500));
}
}
});
and the list goes on
as you see in all my routes I have a try catch block with the possible errors (either only a 500, or a 500/404). And I would like to avoid this repetition.
this is my app.js
const express = require("express");
const bodyParser = require("body-parser");
const createHttpError = require("http-errors");
const api = require("./routes/api");
const app = express();
app.use(express.json());
app.use(bodyParser.json());
app.use("/api", api);
// Catch HTTP 404
app.use((req, res, next) => {
next(createHttpError(404));
});
// Error Handler
app.use((err, req, res, next) => {
res.status(err.status || 500);
res.json({
error: {
status: err.status || 500,
message: err.message,
},
});
});
module.exports = app;
Like I said, it works perfectly now, I would just like to try to avoid the try catch code duplication, and Ive checked the other questions in Stackoverflow but havent helped. The solution ive linked returns a 500 with this catch undefined message (which is not what I want) and on other routes that also have a 404 it just doesnt work.
Thanks a lot!
Update:
I followed Heikos advice but still not working
api.js
const express = require("express");
const createHttpError = require("http-errors");
const Validator = require("../middlewares/Validator");
const TaskNotFoundException = require("../services/TaskNotFoundException");
const TaskService = require("../services/TaskService");
const router = express.Router();
router.get("/tasks", async (req, res, next) => {
const data = await TaskService.getTasks();
res.send({ code: 200, message: "Success", data });
});
app.js
const express = require("express");
const bodyParser = require("body-parser");
const createHttpError = require("http-errors");
const api = require("./routes/api");
const app = express();
app.use(express.json());
app.use(bodyParser.json());
app.use("/api", api);
function catchAsyncErrors(middleware) {
return async function(req, res, next) {
try {
await middleware(req, res, next);
} catch(err) {
next(err);
}
};
}
// Catch HTTP 404
app.use(catchAsyncErrors((req, res, next) => {
next(createHttpError(404));
}));
// Error Handler
app.use(catchAsyncErrors((err, req, res, next) => {
res.status(err.status || 500);
res.json({
error: {
status: err.status || 500,
message: err.message,
},
});
}));
module.exports = app;

Answer 1

If the code inside your async middleware functions contains an await, you must also wrap it in a try-catch block, otherwise a rejected promise will be unhandled. For example:
app.use(async function(req, res, next) {
try {
await Promise.reject("error");
} catch(err) {
next(err);
}
});
propagates the error to the error handler, but without the try-catch block it leads to an "UnhandledPromiseRejection".
You can save some typing if you wrap your middleware into a catchAsyncErrors function:
function catchAsyncErrors(middleware) {
return async function(req, res, next) {
try {
await middleware(req, res, next);
} catch(err) {
next(err);
}
};
}
router.get("/tasks", catchAsyncErrors(async (req, res, next) => {
const data = await TaskService.getTasks();
res.send({ code: 200, message: "Success", data });
}));