So I'm currently learning node.js and express, and I encountered this:

exports.checkBody = checkBody = (req, res, next) => {
  if (!req.body.name || !req.body.price) {
    // Return statement is here
    return res.status(400).json({
      status: "fail",
      message: "Please add a name and price"
    })
  }
  next();
}

Why do I need to put the return statement here, because when I remove the return, it works exactly the same.

Here is the routes

router.post(tourController.checkBody, tourController.createTour);

So I'm currently learning node.js and express, and I encountered this:

exports.checkBody = checkBody = (req, res, next) => {
  if (!req.body.name || !req.body.price) {
    // Return statement is here
    return res.status(400).json({
      status: "fail",
      message: "Please add a name and price"
    })
  }
  next();
}

Why do I need to put the return statement here, because when I remove the return, it works exactly the same.

Here is the routes

router.post(tourController.checkBody, tourController.createTour);

• javascript
• node.js
• express

• So you are wondering why you would not check to see if input is valid and return an error if something is not set? return exits.... – epascarello Commented Aug 14, 2020 at 18:10
• If you remove the return statement, how do you send the error message back to the client? – Barmar Commented Aug 14, 2020 at 18:11
• @Barmar: With res.status(400).json(…). – Ry- ♦ Commented Aug 14, 2020 at 18:11

3 Answers 3

The reason for the return is so you don't execute next() if an error is detected.

The return value isn't important, because res.status() sends the response to the client. So this is actually just a shorthand for doing

exports.checkBody = checkBody = (req, res, next) => {
  if (!req.body.name || !req.body.price) {
    res.status(400).json({
      status: "fail",
      message: "Please add a name and price"
    });
    return;
  }
  next();
}

The return is used for the effect of exiting the function in this case, not for usefully returning a value. It’s a shorter equivalent that some people prefer as a style choice over this:

res.status(400).json({
  status: "fail",
  message: "Please add a name and price"
})
return

If you remove the return entirely, next() will be called, and the next handler will run, which usually isn’t correct after you’ve already responded, and especially not in this case where the middleware being implemented is validation that’s supposed to stop the route from running when validation fails.

I personally prefer the more explicit separate return for the purposes of avoiding exactly this type of confusion, but it doesn’t e up as much anymore now that promises and async + await are available as options.

Because return stops the execution of the function. If there is no return you send the response back but that doesnt mean that the function stops to execute.

Imagine you have some kind of auth middleware that checks if an user is valid and you either send an error back or you move to the next Middleware with next()

Now you dont use return. You get an response on the client that you got rejected but on the serverside the code still got executed. I hope you get what i mean. Its maybe not the best example but... Yea..