javascript node js next

Question

I see a lot of use next in node js   What is it  where does it come from  What does it do  Can I use it client side   Sorry it s used for example here  http   dailyjs com 2010 12 06 node-tutorial-5   look for the loadUser function

User · Accepted Answer

This appears to be a variable naming convention in Node.js control-flow code, where a reference to the next function to execute is given to a callback for it to kick-off when it's done.

See, for example, the code samples here:

http://blog.mixu.net/2011/02/02/essential-node-js-patterns-and-snippets/

Let's look at the example you posted:

function loadUser(req, res, next) {
  if (req.session.user_id) {
    User.findById(req.session.user_id, function(user) {
      if (user) {
        req.currentUser = user;
        return next();
      } else {
        res.redirect('/sessions/new');
      }
    });
  } else {
    res.redirect('/sessions/new');
  }
}

app.get('/documents.:format?', loadUser, function(req, res) {
  // ...
});

The loadUser function expects a function in its third argument, which is bound to the name next. This is a normal function parameter. It holds a reference to the next action to perform and is called once loadUser is done (unless a user could not be found).

There's nothing special about the name next in this example; we could have named it anything.

User · Answer

It s basically like a callback that express js use after a certain part of the code is executed and done  you can use it to make sure that part of code is done and what you wanna do next thing  but always be mindful you only can do one res send in your each REST block     So you can do something like this as a simple next   example   app get       req  res  next    gt      console log  req    req   res    res     res send   data    whatever       next       req  res    gt    console log  it s all done          It s also very useful when you d like to have a middleware in your app        To load the middleware function  call app use    specifying the   middleware function  For example  the following code loads the   myLogger middleware function before the route to the root path        var express   require  express    var app   express     var myLogger   function  req  res  next      console log  LOGGED      next       app use myLogger    app get      function  req  res      res send  Hello World         app listen 3000

User · Answer

It is naming convention used when passing callbacks in situations that require serial execution of actions  e g  scan directory -  read file data -  do something with data  This is in preference to deeply nesting the callbacks  The first three sections of the following article on Tim Caswell s HowToNode blog give a good overview of this   http   howtonode org control-flow  Also see the Sequential Actions section of the second part of that posting   http   howtonode org control-flow-part-ii

[javascript] javascript node.js next()

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