CODEWITHSUNDEEP
javascriptecmascript-6es6-promise
James Roeiter
James Roeiter

Reputation: 861

Chain promises - returned promise resolve does not cause then method to be invoked

I am trying to chain promises but for some reason, my then method is not being called - can not find the reason why, assistance would be much appreciated. The then - .then((decodedTokenData) is not being called but instead the entire promise returned.

let handler = async (event) => {
let accessToken = undefined;
let targetGroup = undefined;
const promise = new Promise(() => {
    accessToken = event.header.authorization;
    targetGroup = event.body.targetGroup;

    let promise = decodeAndVerifyToken(accessToken);
    return promise;
}).then((decodedTokenData) => {
    let isNotGroupMemberResult = isNotGroupMember(decodedTokenData.userGroups);
    return setUserGroup(result.userGroups, targetGroup, userPoolId);
}).then(() => {
    return true;
});
return promise;
}


let decodeAndVerifyToken = (jwtToken) => {
return new Promise((resolve, reject) => {
    jwt.verify(jwtToken, pem, function (err, dToken) {
        if (err) {
            reject(err);
        }

        let userGroups = dToken && dToken["cognito:groups"] ? dToken["cognito:groups"] : [];
        let username = dToken && dToken.username ? dToken.username : null;

        let retval = {
            userGroups,
            username,
            decodedToken: dToken
        }
        resolve(retval);
    })
});
}

let isNotGroupMember = (userGroups) => {
let groupIndex = userGroups.findIndex(groupName => groupName.include(reviewersGroup) || groupName.include(ownersGroup));
let isNotGroupMemberRetval = groupIndex == -1;
return isNotGroupMemberRetval;
}

let setUserGroup = (username, groupname, userPoolId) => {
return new Prmoise((resove, reject) => {
    var params = {
        GroupName: groupname,
        UserPoolId: userPoolId,
        Username: username
    };

    cognitoidentityserviceprovider.adminAddUserToGroup(params, function (err, data) {
        if (err) {
            reject(err);
        } else
            resolve(data);
    });
});
};

EDIT : I understood my problem... I read the following documentation on Mozilla promises : Once a Promise is fulfilled or rejected, the respective handler function (onFulfilled or onRejected) will be called asynchronously (scheduled in the current thread loop). The behaviour of the handler function follows a specific set of rules. If a handler function:

returns a value, the promise returned by then gets resolved with the returned value as its value.

And I thought it applies to both promises and the then method - but it applies only to the then method ...

Upvotes: 0

Views: 80

Answers (2)

avysk
avysk

Reputation: 2035

I'm not sure I understood right what are you doing here, but let me try.

When you do new Promise(() => ...whatever... you create a promise that never resolves, so .then() is never executed. The proper way to create a promise that resolves to some result is new Promise((res) => res(result)).

Example in node:

> const p1 = new Promise(() => 1).then(console.log);
undefined
> p1
Promise { <pending> }
> const p2 = new Promise(res => res(1)).then(console.log);
undefined
> 1

Upvotes: 2

Felix Kling
Felix Kling

Reputation: 816840

new Promise passes resolve and reject to the callback its passed, but you are not making use of it here:

const promise = new Promise(() => {
    accessToken = event.header.authorization;
    targetGroup = event.body.targetGroup;

    let promise = decodeAndVerifyToken(accessToken);
    return promise;
})

This creates a promise that is never resolved. There is no need for new Promise here. Just call decodeAndVerifyToken directly:

decodeAndVerifyToken(event.header.authorization)
  .then((decodedTokenData) => { ... })
  ...

Upvotes: 2

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