Chaining ES6 Promises in Mongoose with Typescript

Add control flow to the existing user by using a existing flag on the promise's response.Example:

public static signup(req: express.Request, res: express.Response) {      UserModel.findOne({ email: req.body.email }).exec()      .then(existingUser => {          if(existingUser) {              return Promise.resolve({                user: existing,                existing: true              });          }          return UserModel.create({              firstName: req.body.firstName,              lastName: req.body.lastName,              email: req.body.email,              password: req.body.password          }).then((user) => {            return Promise.resolve({              existing: false,              user: user            });          });      })      .then(response => {        if (response.existing) {          return res.send({ message: `Email ${response.user.email} is in use` });        } else return res.send({ token: AuthUtils.createJWT(response.user)});      })      .catch(err => {          console.log(err);      });  }

I actually ended up building my project for ES6 so that I could use async/await

It allowed me to simplify the code drastically.

public static async signup(req: express.Request, res: express.Response) {    try {        let user = await UserModel.findOne({ email: req.body.email }).exec()        if(user) {            throw `Email ${user.email} is in use`;        }        if(environment.debug) console.log(`Creating new user ${req.body.firstName} ${req.body.lastName} with email ${req.body.email}`);        user = await UserModel.create({            firstName: req.body.firstName,            lastName: req.body.lastName,            email: req.body.email,            password: req.body.password        });        return res.send({ token: AuthUtils.createJWT(user)});    } catch(e) {        console.log(e);        res.send({ error: e });    }}