The express framework has a default error handler, that catches and processes errors that occur synchronously and asynchronously.
But the express default error handler returns an error in the HTML page. To fix this, I'll add an error middleware in my app.
For this series, I'm following an excellent video tutorial from Traversy Media
Table Of Contents
Implement errorMiddleware
Create a file named as errorMiddleware.js
in /backend/middleware
folder and add this code.
const errorHandler = (err, req, res, next) => {
const statusCode = res.statusCode ? res.statusCode : 500;
res.status(statusCode);
res.json({
message: err.message,
stack: err.stack,
});
};
module.exports = {
errorHandler,
};
and now I'll add it into server.js
file.
const { errorHandler } = require('./middleware/errorMiddleware');
...
app.use(errorHandler);
...
Make sure to define error-handling middleware in the last, after other app.use().
You can read more about it here
Now I'll test the errorMiddleware in my setTodo POST call
const setTodo = (req, res) => {
if (!req.body.text) {
res.status(400);
throw new Error('Please add text field');
}
res.status(200).json({message: 'Set todo'})
}
and I'll get this error response
Implement asyncHandler
As I am going to use mongoose
in my next blog to interact with the database, which returns a promise in response. So to handle this I'll use async/await
in all of the todosController
functions.
For async/await
we have to use a try/catch
method but as I already have an error handler so I'll use express-async-handler
package.
This package will handle the exceptions inside of async express routes and pass them to my express error handlers.
Install async handler with this command
npm i express-async-handler
Now use it like this for all functions in todosController.js
const asyncHanlder = require('express-async-handler');
const getTodos = asyncHanlder(async (req, res) => {
res.status(200).json({message: 'Get todos'})
});
...
In the next blog, I'll create a database in MongoDB and connect it with Mongoose.
Thank you for reading!
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