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The next function is a function in the Express router which, when invoked, executes the middleware succeeding the current middleware. Middleware functions can perform the following tasks: Execute any code. Make changes to the request and the response objects.
next() : It will run or execute the code after all the middleware function is finished. return next() : By using return next it will jump out the callback immediately and the code below return next() will be unreachable.
To achieve this, you can use a simple but efficient pattern: wrap your actual middleware function with a second one that receives the desired parameters, like so. Then, simply pass the desired parameter to the middleware wrapper function when passing to the Express routes.
Error-handling middleware always takes four arguments. You must provide four arguments to identify it as an error-handling middleware function.
This is what the res.locals object is for. Setting variables directly on the request object is not supported or documented. res.locals is guaranteed to hold state over the life of a request.
res.locals
An object that contains response local variables scoped to the request, and therefore available only to the view(s) rendered during that request / response cycle (if any). Otherwise, this property is identical to app.locals.
This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on.
app.use(function(req, res, next) {
res.locals.user = req.user;
res.locals.authenticated = !req.user.anonymous;
next();
});
To retrieve the variable in the next middleware:
app.use(function(req, res, next) {
if (res.locals.authenticated) {
console.log(res.locals.user.id);
}
next();
});
Attach your variable to the req object, not res.
Instead of
res.somevariable = variable1;
Have:
req.somevariable = variable1;
As others have pointed out, res.locals is the recommended way of passing data through middleware.
I don't think that best practice will be passing a variable like req.YOUR_VAR. You might want to consider req.YOUR_APP_NAME.YOUR_VAR or req.mw_params.YOUR_VAR.
It will help you avoid overwriting other attributes.
Update May 31, 2020
res.locals is what you're looking for, the object is scoped to the request.
An object that contains response local variables scoped to the request, and therefore available only to the view(s) rendered during that request / response cycle (if any). Otherwise, this property is identical to app.locals.
This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on.
That's because req and res are two different objects.
You need to look for the property on the same object you added it to.
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