What is the functionality of Promises in this code?

Question

What is the functionality of Promises in this code?

I am curious about some aspects of the code snippet provided below:

getRemoteProfile seems to return Promise.resolve only under specific conditions, but what happens if that condition fails since getRemoteProfile calls are always chained with then?

Can you explain the difference between return promise and return promise.resolve? It appears that return promise.resolve always leads to the execution of then.

function getRemoteProfile(id) {
    if (!id && /^_/.test(id)) {
        return Promise.resolve(null);
    }
    var isGroup = app.isGroupId(id);
    if (isGroup) {
        return getGroupInfo(id);
    } else {
        return getUserInfo(id.split('@')[0], app.currentUserDomain);
    }
}

function reloadProfile(id, keep) {
    return getRemoteProfile(id).then(function(contactProfile) {
        // var isGroup = app.isGroupId(id);
        if (contactProfile) {
            contactProfile.contact_id = id;
            if (!keep) {
                delete profilePromises[id];
            }
            contactProfile.member = true;
            updateProfile(contactProfile.contact_id, contactProfile).then(function() {
                app.imagesStorage.setContactIcon(contactProfile.contact_id);
            });

            return setDetails(contactProfile);
        }
    });
}

javascript promise

Answer 1

Answer №1

When calling the <code>.then method, ensure that the objects being operated on have the necessary .then properties. If the getRemoteProfile function returns anything other than a Promise, an error will likely be thrown.

However, in this particular scenario, if there are no indications of code malfunctions, it is highly probable that both getGroupInfo and getUserInfo functions create and return Promises on their own. Therefore, getRemoteProfile does not need to generate one for them.

Usually, Promise.resolve is used when a Promise is required but there is no actual need for an asynchronous operation, such as a network request, in the current situation.

Answer 2

When calling the <code>.then method, ensure that the objects being operated on have the necessary .then properties. If the getRemoteProfile function returns anything other than a Promise, an error will likely be thrown.

However, in this particular scenario, if there are no indications of code malfunctions, it is highly probable that both getGroupInfo and getUserInfo functions create and return Promises on their own. Therefore, getRemoteProfile does not need to generate one for them.

Usually, Promise.resolve is used when a Promise is required but there is no actual need for an asynchronous operation, such as a network request, in the current situation.

Answer 3

Answer №2

When using getRemoteProfile, the function only resolves for one specific condition. What happens if the condition is not met when the function is called with .then?

It can be assumed that both getGroupInfo and getUserInfo also return promises, and the getRemoteProfile function will always enter one of the conditional branches that returns a value. Since all promises have a .then method, as long as the function consistently returns a promise, it should work correctly.

What is the difference between returning a promise and returning promise.resolve? My understanding is that returning promise.resolve always triggers the .then method.

The function Promise.resolve actually creates a promise, so when you return Promise.resolve(...), you are indeed returning a promise.

Answer 4

When using getRemoteProfile, the function only resolves for one specific condition. What happens if the condition is not met when the function is called with .then?

It can be assumed that both getGroupInfo and getUserInfo also return promises, and the getRemoteProfile function will always enter one of the conditional branches that returns a value. Since all promises have a .then method, as long as the function consistently returns a promise, it should work correctly.

What is the difference between returning a promise and returning promise.resolve? My understanding is that returning promise.resolve always triggers the .then method.

The function Promise.resolve actually creates a promise, so when you return Promise.resolve(...), you are indeed returning a promise.

What is the functionality of Promises in this code?

Answer №1

Answer №2

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