Passing variables to the next middleware using next in Express js

Question

Well  my question is I want to pass some variable from the first middleware to another middleware  and I tried doing this  but there was  req somevariable is a given as  undefined         app js    app get   someurl    middleware1  middleware2              middleware1     some conditions     res somevariable   variable1  next                middleware2     some conditions     variable   req somevariable

User · Accepted Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

The trick is pretty simple    The request cycle is still pretty much alive  You can just add a new variable that will create a temporary  calling  app get  some url endpoint   middleware1  middleware2     Since you can handle your request in the first middleware   req  res  next    gt        var yourvalue   anyvalue     In middleware 1 you handle your logic and store your value like below   req anyvariable   yourvalue   In middleware 2 you can catch this value from middleware 1 doing the following    req  res  next    gt        var storedvalue   req yourvalue

User · Answer

As mentioned above  res locals is a good  recommended  way to do this  See here for a quick tutorial on how to do this in Express

[javascript] Passing variables to the next middleware using next() in Express.js

Examples related to javascript

Examples related to node.js

Examples related to express

Examples related to middleware

Examples related to next