只回最里面的承诺，抓住和处理别人

Question

我有以下情况：

savePicture(newPicture, fileData){
    return compressionUtil.makePictureAndThumbnail(newPicture).then((data) => {
        let writeBig = fsUtil.writeFileToDisk(pictureFileName, data[0])
        let writeSmall = fsUtil.writeFileToDisk(thumbnailFileName, data[1])

        return Promise.all([writeBig, writeSmall]).then(() => {
            let picToSave = {
                uploaderUsername: fileData.username,
                directory: fileDirectory,
                fileName: fileName,
                tags: fileData.tags,
                description: fileData.description,
                droneTaken: fileData.droneTaken,
                isGenuine: isGenuine,
                metadata: metadata
            }
            return Picture.create(picToSave)
        })
    })
}

我想做的是处理可能拒绝compressionUtil.makePictureAndThumbnail()和Promise.all([writeBig, writeSmall])的承诺，就像这样

savePicture(newPicture, fileData){
    return compressionUtil.makePictureAndThumbnail(newPicture).then((data) => {
        let writeBig = fsUtil.writeFileToDisk(pictureFileName, data[0])
        let writeSmall = fsUtil.writeFileToDisk(thumbnailFileName, data[1])

        return Promise.all([writeBig, writeSmall]).then(() => {
            let picToSave = {
                uploaderUsername: fileData.username,
                directory: fileDirectory,
                fileName: fileName,
                tags: fileData.tags,
                description: fileData.description,
                droneTaken: fileData.droneTaken,
                isGenuine: isGenuine,
                metadata: metadata
            }
            return Picture.create(picToSave)
        }).catch((err)=>{/*Handle promise.all error here*/})
    }).catch((err)=>{/*Handle makePictureAndThumbnail error here*/})
}

但同时，让savePicture()只返回Picture.create()的诺言.then()和.catch()。

我想的是把它包装在一个巨大的新承诺((决心，拒绝)=>{})，但这可能是一个可怕的做法。

关于这方面的投入是非常感谢的。谢谢。

Answer 1

用一个巨大的新承诺((解决，拒绝)=>{})来包装这一切可能是一种可怕的做法。

是的indeed it is！

要处理来自承诺而不是then实现回调的拒绝，可以使用.then(…).catch(…)

savePicture(newPicture, fileData){
    return compressionUtil.makePictureAndThumbnail(newPicture).then((data) => {
        …
        return …
    }, err => {
//   ^ no `catch`
        /* Handle makePictureAndThumbnail error here */
    });
}

类似地，

return Promise.all([writeBig, writeSmall]).then(() => {
    let picToSave = { … }
    return Picture.create(picToSave);
}).catch(err => {
    /* Handle all errors from writeBig, writeSmall and create */
});

​

return Promise.all([writeBig, writeSmall]).then(() => {
    let picToSave = { … }
    return Picture.create(picToSave).catch(err => {
        /* Handle errors from create */
    });
}, err => {
    /* Handle all errors from writeBig and writeSmall */
});