값을 얻기 위해 객체를 반복해야하므로 for 루프와 약속에 문제가 있습니다.

두 가지 대안 :

비동기 호출이 병렬로 실행될 수있는 경우 (100 개가 있더라도 상관 없음) 다음 을 사용할 수 있습니다 Promise.all.

let previewMessages = [];
let promises = [];

// Build the array of promises
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {};
    previewMessages.push(messageObj);

    messageObj.timeStamp = message.context.latestPost;
    messageObj.user = message.context.otherUsername;
    messageObj.picture = message.context.itemImageURL;
    promises.push(getItemsById([message.context.itemID]).then(itemInfo => {
        messageObj.title = itemInfo[Object.keys(itemInfo)[0]].title;
    }));
}
// Wait for them all to complete
Promise.all(promises).then(() => {
    // use previewMessages
});

그들이 경우 이 순서로, 다음을 수행하기 전에 각각 기다립니다

let previewMessages = [];
let promise = Promise.resolve();

// Loop through building up the `then` chain
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {};
    previewMessages.push(messageObj);

    // This one will wait for the next
    promise = promise.then(() => {
        messageObj.timeStamp = message.context.latestPost;
        messageObj.user = message.context.otherUsername;
        messageObj.picture = message.context.itemImageURL;
        return getItemsById([message.context.itemID]).then(itemInfo => {
            messageObj.title = itemInfo[Object.keys(itemInfo)[0]].title;
        });
    });
}
// Wait for the last one to complete
promise.then(() => {
    // Use previewMessages
});

그러나 기다릴 필요가없는 값을 채우기 위해 리터럴을 사용할 것입니다.

비동기 :

let previewMessages = [];
let promises = [];

// Build the array of promises
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {
        timeStamp: message.context.latestPost,
        user: message.context.otherUsername,
        picture: message.context.itemImageURL
    };
    previewMessages.push(messageObj);

    promises.push(getItemsById([message.context.itemID]).then(itemInfo => {
        messageObj.title = itemInfo[Object.keys(itemInfo)[0]].title;
    }));
}
// Wait for them all to complete
Promise.all(promises).then(() => {
    // use previewMessages
});

동조:

let previewMessages = [];
let promise = Promise.resolve();

// Loop through building up the `then` chain
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {
        timeStamp: message.context.latestPost,
        user: message.context.otherUsername,
        picture: message.context.itemImageURL
    };
    previewMessages.push(messageObj);
    // This one will wait for the next
    promise = promise.then(() => {
        return getItemsById([message.context.itemID]).then(itemInfo => {
            messageObj.title = itemInfo[Object.keys(itemInfo)[0]].title;
        });
    });
}
// Wait for the last one to complete
promise.then(() => {
    // Use previewMessages
});

간단하고 실행 가능한 한 쌍의 예제가 도움이 될 것입니다. 또한 "... 문제는 func2가 func1에서 반환 객체를 가져 간다는 것입니다 ..."라고 언급 했으므로이를 믹스에 추가해 보겠습니다.

평행:

const messages = {
    "one": {name: "Message one"},
    "two": {name: "Message two"},
    "three": {name: "Message three"},
    "four": {name: "Message four"}
};

let previewMessages = [];
let promises = [];

// Build the array of promises
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {
        name: message.name
    };
    previewMessages.push(messageObj);

    promises.push(func1(message).then(func2).then(info => {
        messageObj.info = info;
    }));
}
// Wait for them all to complete
Promise.all(promises).then(() => {
    // use previewMessages
    console.log("Done! Result:", previewMessages);
});

function func1(message) {
    return new Promise(resolve => {
        // Use setTimeout for async
        setTimeout(() => {
            console.log("func1 resolving on " + message.name);
            resolve(message.name + " - func1");
        }, Math.random() * 500);
    });
}
function func2(info) {
    return new Promise(resolve => {
        // Use setTimeout for async
        setTimeout(() => {
            console.log("func2 resolving on " + info);
            resolve(info +  " - func2");
        }, Math.random() * 500);
    });
}

.as-console-wrapper {
  max-height: 100% !important;
}

순서:

const messages = {
    "one": {name: "Message one"},
    "two": {name: "Message two"},
    "three": {name: "Message three"},
    "four": {name: "Message four"}
};

let previewMessages = [];
let promise = Promise.resolve();

// Build the promise chain
for (let messageID in messages) {
    let message = messages[messageID];
    let messageObj = {
        name: message.name
    };
    previewMessages.push(messageObj);

    promise = promise.then(() => func1(message).then(func2).then(info => {
        messageObj.info = info;
    }));
}
// Wait for the last one to finish
promise.then(() => {
    // use previewMessages
    console.log("Done! Result:", previewMessages);
});

function func1(message) {
    return new Promise(resolve => {
        // Use setTimeout for async
        setTimeout(() => {
            console.log("func1 resolving on " + message.name);
            resolve(message.name + " - func1");
        }, Math.random() * 500);
    });
}
function func2(info) {
    return new Promise(resolve => {
        // Use setTimeout for async
        setTimeout(() => {
            console.log("func2 resolving on " + info);
            resolve(info +  " - func2");
        }, Math.random() * 500);
    });
}

.as-console-wrapper {
  max-height: 100% !important;
}