Nested handlers

[Jbarget]

https://github.com/fac-12/BudgetPlanner/blob/master/src/handler.js#L91-L126

Typically this is a prime use case for promises (but know that you only dabbled with that a little this week). This is a bit tricky, and hard to test, what you'll want to do here is create new functions that you pass in as arguments instead of nesting.

eg.

const createUserHandler = (err, res) => {
    if (err) {
       response.writeHead(500, { 'content-type': 'text/html' });
       response.end('Oops! There was a problem');
   } else {
      let userIdName = JSON.parse(res);
      const cookie = sign(userIdName, process.env.SECRET);
      response.writeHead(302, { 'Location': '/main', 'Set-Cookie': `jwt=${cookie}; HttpOnly` });
      response.end('You have succesfully signed in');
   }
}

if (validateUser(userData) === true) {
   checkUser(userData, (err, res) => {
      if (err) {
         response.writeHead(500, { 'content-type': 'text/html' });
         response.end('Oops! There was a problem');
      } else if (res === 1) {
         response.writeHead(401, { 'content-type': 'text/html' })
         response.end(`Username: ${userData.username} already exists, try logging in`);
     } else if (res === 0) {
         genHashedPassword(userData, (err, result) => {
          if (err) {
            response.writeHead(500, { 'content-type': 'text/html' });
            response.end('Oops! There was a problem');
         } else {
             createUser(result, createUserHandler);
         }
      });
   }
});