javascript - Before filter for all post requests in node.js -

i have below code in node.js app.js:

var express = require('express')     ,cors = require('cors')     ,app=express();     var users = require('./routes/users');     //some other codes     .....     app.use('/', routes);     app.use('/users', users ); 

if request made /users/adduser, go users.js in routes folder.

now want add filter capture post requests , validations , if conditions satisfied post should go handler.

i.e if /users/adduser post request, before going method in users.js in routes folder, should able capture request , stop if condition not met.

update 1 having app.use function, in result getting undefined not waiting till function returning value

app.use(function (req, res, next) {     req.db = db;     if (req.method != "post") {         next();     }     else {         var userdata = req.body;         var result = check(userdata);         if(result){         next();                     }     } });  function check(userdata) {       var url = "someurl"+userdata.id;      var request = require("request");     request({         url: url,         json: true     }, function (error, response, body) {          if (!error && response.statuscode === 200) {             if (response.tojson().body.id == userid) {                  return true;                 // tried next();             }           }     }) }; 

you can write simple middleware function that:

var validator = function(req, res, next) {   // if request wasn't post request, pass along next handler immediately.   if (req.method !== 'post') return next();    // perform validations.   check(req.body, function(err) {     // validation failed, or error occurred during external request.     if (err) return res.sendstatus(400);     // validation passed.     return next();   }); };  function check(userdata, callback) {    var url     = "someurl"+userdata.id;   var request = require("request");   request({ url: url, json: true }, function(error, response, body) {     if (!error && response.statuscode === 200) {       if (response.tojson().body.id === userid) {          return callback(null, true);       }     }     return callback(new error());   }) }; 

you have various points @ can insert middleware, kind of depend on how app structured.

one option:

app.use('/users', validator, users); 

or, if have separate router /users (in ./routes/users.js):

router.use(validator); 

or, if have separate post route /users/adduser:

router.post('/adduser', validator, function(req, res) { ... }); 

in last case don't have check req.method in validator middleware because it's limited post handler anyway.