How to return a variable along with the promise from a javascript function?

Question

This is where I am stuck:

var verifyEmp = async function () {
    return 'Verified';
}


Employee.find(email, password)
.then((emp) => {
    console.log(emp);
    return verifyEmp();
})
.then((msg) => {
    console.log({ verificationMsg: msg });
})
.catch((err) => {
    console.log(err);
})

As you can see, verifyEmp is a promise returning function(For demo purposes, I have kept this function as simple as possible). So, what I want to achieve is to be able to log { Emp: emp, verificationMsg: msg } in my second then. How do I pass emp variable in the second then while returning the promise.

I know this is conveniently achievable via async/await. I am just exploring how it can be done using traditional promises.

But you are still using async in your code, more so without await — Anurag Srivastava
– Anurag Srivastava, Commented Mar 28, 2020 at 16:33
You can just do Promise.resolve(employeeObject) in your first .then, and it will be available in your second .then. — Utsav Patel
– Utsav Patel, Commented Mar 28, 2020 at 16:35
@AnuragSrivastava, yes I know. Please just assume that I don't want to use async/await in my other function. I want to know whether this thing is achievable using traditional promises or not. — JessePinkman
– JessePinkman, Commented Mar 28, 2020 at 16:43
@UtsavPatel, I have to get to the second then to resolve the VerifyEmp promise so that I can get that 'verified' msg. I can't resolve { emp: emp, verificatonMsg: msg } in the first then because I don't have verificationMsg yet. — JessePinkman
– JessePinkman, Commented Mar 28, 2020 at 16:46

Mark · Accepted Answer · 2020-03-28 16:43:09Z

1

If you just want to use promises, you can nest a then() into the second one that resolves with the result of the first:

const verifyEmp = async function () {
    return 'Verified';
}

const Employee = {
    async find() {
        return "An employee"
    }
}

Employee.find()
.then(emp => verifyEmp().then(msg => [emp, msg]))
.then(([emp, msg]) => {
    /* do something with amp and msg */
    console.log({emp: emp, verificationMsg: msg });
})
.catch((err) => {
    console.log(err);
})

answered Mar 28, 2020 at 16:43

Mark

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Comments

Amardeep Bhowmick · Accepted Answer · 2020-03-28 16:56:26Z

You can return the Promise result from the verifyEmp().then() call (as async functions return a Promise) from the first find().then callback.

There you can pass both the result of the verifyEmp() call and also the emp object from the current scope wrapped in another object to the next then in the chain.

The Promise from the verifyEmp().then() gets automatically unwrapped in the next then callback in the chain:

var verifyEmp = async function () {
    return 'Verified';
}

const Employee = {
  find: async function(email, password){
    return {email, password, "id":123};
  }
}

Employee.find("[email protected]", "test")
.then((emp) => {
    //This promise woud get unwrapped in the next .then callback
    return verifyEmp()
           .then((msg) => ({emp,msg}));
})
.then((msg) => {
    console.log(msg);
})
.catch((err) => {
    console.error(err);
})

ibrahim tanyalcin · Accepted Answer · 2020-03-28 16:41:29Z

0

Didn't test it. Use an async iife or something of sort, if you hate anti-patterns. This solution will work regarless of verifyEmp returning a promise or not.

var verifyEmp = async function () {
    return 'Verified';
}


Employee.find(email, password)
.then((emp) => {
    console.log(emp);
    return (async function(){return verifyEmp()})().then((ver)=>[emp,ver]);
})
.then((msg) => {
    console.log({ verificationMsg: msg });
})
.catch((err) => {
    console.log(err);
})

answered Mar 28, 2020 at 16:41

ibrahim tanyalcin

6,5634 gold badges21 silver badges27 bronze badges

2 Comments

jfriend00 Over a year ago

This makes no sense. First off, you will know whether verifyEmp() returns a promise or not. If you don't, then something else is wrong. If you really want to wrap the return value of verifyEmp() in a promise, then just do this Promise.resolve(verifyEmp()).then(ver => [emp,ver]). There's no reason for the extra async function.

jfriend00 Over a year ago

It's not about typing savings, it's about writing code that is declarative and is obvious what/why it's written that way. I say again, if you don't know what something returns, that's a serious problem. If you actually are trying to use a function that sometimes returns a promise and sometimes returns a value, then throw that library away as that's a broken interface or fix the code. A sometimes asynchronous interface should always return a promise.

boyddddd · Accepted Answer · 2020-03-28 17:05:17Z

0

Just return json object instead of string.

var verifyEmp = async function () {
    return 'Verified';
}


Employee.find(email, password)
.then((emp) => {
    console.log(emp);
    return {emp:emp, msg:verifyEmp()};
})
.then((res) => {
    console.log({ Emp: res.emp, verificationMsg: res.msg });
})
.catch((err) => {
    console.log(err);
})

answered Mar 28, 2020 at 17:05

boyddddd

1

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