what's the different between app.post and app.use in nodes express?

app.use() is use to include middleware/interceptor function that will be executed before the actual function will executed when an api is call .

for more details refer - express offcial website

for example :

app.use(cors());    app.post("/",function(req,res){    });

The above line of code is equivalent to

app.post("/",cors(),function(req,res){});

app.post , app.get , app.put , app.delete define the http method for the api .
please refer link http://www.tutorialspoint.com/http/http_methods.htm for more details about http methods

In your case

app.use(bodyParser.json());app.use(bodyParser.urlencoded({    extended: true}));app.post('/add_module', function(req, res) {    console.log("Start submitting");    console.log(req.body);}

when /add_module api is called , first bodyParser.json() then bodyParser.urlencoded({ extended: true }) function is called after that

 function(req, res) {        console.log("Start submitting");        console.log(req.body);} 

is called .bodyParser.json() and bodyParse.urlencoded({extended:true}) is required get body object from request in the called function(req,res)

It's the quite the same but :

• middleware included in app.use will be use in all request

• middleware included in app.post("/route" will be use only for request of type POST wich match the path /route

Example, if you server contains the following :

 // Common middleware app.use(function(req, res, next){    console.log("Middleware1");    return next(); }); app.use(function(req, res, next){    console.log("Middleware2");    return next(); }); // POST middleware app.post("/api/test1", function(req, res, next){    console.log("Middleware3");    return next(); }) app.post("/api/test2", function(req, res, next){    console.log("Middleware4");    return next(); }) // Actions app.post("/api/test1", function(req, res, next){    console.log("finalPOSTAction1");    return res.status(200).json({}); }) app.post("/api/test2", function(req, res, next){   console.log("finalPOSTAction2");   return res.status(200).json({}); }) app.get("/api/test3", function(req, res, next){   console.log("finalGETAction3");   return res.status(200).json({}); })

A request GET on /api/test3 will raise the following :

- Middleware1- Middleware2- finalGETAction3

A request POST on /api/test1 will raise the following :

- Middleware1- Middleware2- Middleware3- finalPOSTAction1

And a request POST on /api/test2 will raise the following :

- Middleware1- Middleware2- Middleware4- finalPOSTAction2