[英]Promise not get resolved with async
我正在使用igmur api上传图像。 我使用Promises(异步等待)在Node.js中编写了一个应用程序。 (请注意,我对这些概念还很陌生)。
我的代码似乎确实有效。 它将图像上传到igmur。 但是,问题是,诺言没有得到解决。 请参考下面的代码。
router.post('/images/upload', async (req, res) => {
/* we would receive a request of file paths as array */
let filePaths = req.body.urls;
let multipleUpload = new Promise(async (resolve, reject) => {
let upload_len = filePaths.length,
upload_res = new Array();
for (let i = 0; i <= upload_len + 1; i++) {
let filePath = filePaths[i];
await imgur.upload(filePath, (error, result) => {
console.log(" A -> ");
if (upload_res.length === upload_len) {
console.log("******");
/* resolve promise after upload is complete */
resolve(upload_res)
} else if (result) {
/*push public_ids in an array */
console.log("OK")
upload_res.push(result.public_id);
} else if (error) {
console.log(error)
reject(error)
}
})
}
})
.then((result) => console.log(result))
.catch((error) => error)
let upload = await multipleUpload;
res.json({
'response': upload
})
})
我至少看到两个问题:
imgur.upload
没有返回Promise,因为它接受了回调函数。 我认为这应该解决它:
router.post('/images/upload', async (req, res) => {
let filePaths = req.body.urls
let upload_len = filePaths.length
let multipleUpload = filePaths.map(filePath => {
return new Promise((resolve, reject) => {
imgur.upload(filePath, (err, result) => {
if (err) {
reject(err)
} else {
resolve(result.public_id)
}
})
})
})
let upload = await Promise.all(multipleUpload)
res.json({
response: upload,
})
})
一个(非常)更高效的代码版本是:
function uploadToImgur(filePath) {
return new Promise((resolve, reject) => {
imgur.upload(filePath, (err, res) => {
if (err) reject(err);
resolve(res.public_id);
})
})
}
router.post('/images/upload', async (req, res) => {
/* we would receive a request of file paths as array */
let filePaths = req.body.urls;
let promises = filePaths.map(uploadToImgur);
let upload = await Promise.all(promises);
res.json({
'response': upload
})
})
这使用Array.map
创建一个诺言数组,一个诺言对应于每个filePath
,然后使用Promise.all
同时等待所有诺言。
修正逻辑,以便在推送result
后检查length
。 你从不叫resolve
。
例如,如果收到1个文件,则将推入数组,然后退出循环。
if (result) {
/*push public_ids in an array */
console.log("OK")
upload_res.push(result.public_id);
if (upload_res.length === upload_len) {
console.log("******");
/* resolve promise after upload is complete */
resolve(upload_res)
}
}
在另一个主题上,您应该在发生错误后退出循环,否则您可能最终会调用拒绝,然后解决,这不好。
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