unresolved function or method

the problem is that these properties are not defined in Express module - they are added dynamically in runtime. That's why WebStorm can't resolve them using static analysis.

As a workaround you can try installing 'express', 'serve-static' and 'express-serve-static-core' Typescript stubs via Settings | Languages & Frameworks | JavaScript | Libraries, Download...

Now it compiles, but I keep getting "Cannot GET /addUser" or about delete. 

this error is shown as you didn't instruct your server how to respond on GET /addUser. You need adding

app.get('/addUser', function (req, res) {//your code here

I copy/pasted my code, and as I have said - get works but post doesn't. So if at the begging post didn't *compile*, now it doesn't *work* (also deleteUser doesn't work).

The full (un-working) code:  

var express = require('express');
var app = express();
var fs = require("fs");

var user = {
    "user4" : {
        "name" : "mohit",
        "password" : "password4",
        "profession" : "teacher",
        "id": 4
    }
}

app.post('/addUser', function (req, res) {
    // First read existing users.
    fs.readFile( __dirname + "/" + "users.json", 'utf8', function (err, data) {
        data = JSON.parse( data );
        data["user4"] = user["user4"];
        console.log( data );
        res.end( JSON.stringify(data));
    });
})


var server = app.listen(8082, function (err ) {
    var host = server.address().address
    var port = server.address().port
    console.log("Example app listening at http://%s:%s", host, port)

})

Please see my previous reply:) If you need an advise of developing your Express app, I'd suggest asking on StackOverflow - this forum is mostly intended for discussing IDE problems

I'm sorry I keep nagging, but the thing is - I saw your previous replay, that said 

app.get('/addUser', function (req, res) {//your code here

The thing is - in my code I should enter 

app.post('/addUser', function (req, res) {

("post" and not "get"). So still "get" works but "post" doesn't. Is the guide wrong?

let me explain... When you open http://localhost:8082/addUser in browser, you perform a GET request your server should handle... But you don't have any code that handles this request - the only method you have handles POST. You can try some REST client to post a request to your server - it will respond with expected JSON. But GET request will fail

Ohhh I thought that Chrome can be the client... Thank you!