Lets say i want to run an if statment where the condition is async function.

const con = require('./con');

if(con.con('[email protected]')
  console.log('User exists!')
else {
  console.log('user does not exist?')
}

This is the function, it uses mongoose findOne which is an async task.

const User = require ('../nodeDB/models/user.js');

const con = function (email) {
     User.findOne( { userEmail: email }, function (err, doc) {
       if(err) {
           console.log(err);
       }
       
       if (doc) {
           return false;
       } else {
           return true;
       }
     });
}

module.exports.con = con;

The problem is that the if statment gets called before the con can get executed which then does'nt set the condition.

CodePudding user response：

You can do it this way :

const con = userEmail => User.findOne({userEmail}).lean().exec();

(async () => {
    if (await con('[email protected]')) {
        console.log('User exists!')
    } else {
        console.log('user does not exist?')
    }
})()

1. Return User.findOne from your function.

(optional) 2. Add it .lean() (returns simple JSON, faster)

(optional) 3. Add it .exec() so it returns a true Promise and not just a thenable

4. now you can simply await con() anywhere inside an async function, just as if it was synchronous.

CodePudding user response：

Firstly your con() function doesn't return anything. You will need to return User.findOne(....)

Your if statement needs to respect the fact that the async task has to complete first.

con.con('[email protected]')
  .then((exists) => {
     if (exists)
       console.log('User exists!')
     else {
       console.log('user does not exist?')
     }
  })

Or with aynsc/await:

async function checkIfUserExists() {
  if (await con.con('[email protected]')
    console.log('User exists!')
  else {
    console.log('user does not exist?')
  }
}

CodePudding user response：

Use await or put your logic in then block.

// must be in async declared function
if (await foo()) {
}
else {
}

// or 

foo().then(res=>{
  if (res) {
  }
  else {
  }
})