blocks|key|2446597|text|首先，您构造了writeFilePromise和mkDirPromise，以便它们始终是resolve，而不是reject。因为fs.writeFile和fs.mkdir是异步的，所以一旦它们启动，线程就会立即转移到resolve()。我想你的意思是..。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2446598|function+writeFilePromise(writePath,+textContent)+{
++++return+new+Promise((resolve,+reject)+=>+{
++++++++fs.writeFile(writePath,+textContent,+(err)+=>+{
++++++++++++if+(err)+reject();
++++++++++++else+resolve();
++++++++});
++++});
}

function+mkDirPromise(dir)+{
++++return+new+Promise((resolve,+reject)+=>+{
++++++++fs.mkdir(path.join(constants.FILES_STORAGE_DIR,+dir),+(err)+=>+{
++++++++++++if+(err)+reject();
++++++++++++else+resolve();
++++++++});
++++});
}|code-block|syntax|javascript|2446599|就fs.exists而言，它已经过时了，所以我不推荐使用它。相反，可以尝试使用fs.access|2446600|function+accessPromise(dir)+{
++++return+new+Promise((resolve,+reject)+=>+{
++++++++fs.access(dir,+(err)+=>+{
++++++++++++if+(err)+reject();
++++++++++++else+resolve();
++++++++});
++++});
}|2446601|最后，尝试调整使用async函数声明的位置，以确保正确地同步代码：|2446602|async+function+createFile(dir,+fileName,+httpMethod,+textContent)+{
++++const+searchPath+=+path.join(ROOT_DIR,+dir,+fileName);
++++if+(httpMethod+===+POST+&&+await+accessPromise(searchPath))+{
++++++++return+false;
++++}+else+{
++++++++const+fileExistsStatus+=+await+accessPromise(path.join(ROOT_DIR,+dir));
++++++++try+{
++++++++++++if+(!fileExistsStatus)+{
++++++++++++++++await+mkDirPromise(dir);
++++++++++++}
++++++++++++await+writeFilePromise(searchPath,+textContent);
++++++++++++return+true;
++++++++}+catch+(err)+{
++++++++++++return+false;
++++++++}
++++}
}|2446603|记得在调用该函数时使用await+createFile(dir,+fileName,+httpMethod,+textContent)。|2446604|entityMap^0|7|G|O|C|18|7|1J|6|1S|C|25|8|30|9|0|0|1|9|13|9|0|0|9|5|0|0|B|1K|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1H|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1L|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1M|8|@$9|1N|A|1O|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|V|$]]

First of all, you've structured <code>writeFilePromise</code> and <code>mkDirPromise</code> so that they will always <code>resolve</code>, and never <code>reject</code>. Since <code>fs.writeFile</code>
and <code>fs.mkdir</code> are asynchronous, the thread immediately moves on to <code>resolve()</code> once they've kicked off. I think what you meant was...

<pre><code>function writeFilePromise(writePath, textContent) {
 return new Promise((resolve, reject) =&gt; {
 fs.writeFile(writePath, textContent, (err) =&gt; {
 if (err) reject();
 else resolve();
 });
 });
}

function mkDirPromise(dir) {
 return new Promise((resolve, reject) =&gt; {
 fs.mkdir(path.join(constants.FILES_STORAGE_DIR, dir), (err) =&gt; {
 if (err) reject();
 else resolve();
 });
 });
}
</code></pre>

In terms of <code>fs.exists</code>, that's been depricated, so I wouldn't recommend using it. Instead, try <code>fs.access</code>:

<pre><code>function accessPromise(dir) {
 return new Promise((resolve, reject) =&gt; {
 fs.access(dir, (err) =&gt; {
 if (err) reject();
 else resolve();
 });
 });
}
</code></pre>

Finally, try adjusting where you use the <code>async</code> function declaration, to ensure you're synchronizing your code correctly:

<pre><code>async function createFile(dir, fileName, httpMethod, textContent) {
 const searchPath = path.join(ROOT_DIR, dir, fileName);
 if (httpMethod === POST &amp;&amp; await accessPromise(searchPath)) {
 return false;
 } else {
 const fileExistsStatus = await accessPromise(path.join(ROOT_DIR, dir));
 try {
 if (!fileExistsStatus) {
 await mkDirPromise(dir);
 }
 await writeFilePromise(searchPath, textContent);
 return true;
 } catch (err) {
 return false;
 }
 }
}
</code></pre>

Remember to use <code>await createFile(dir, fileName, httpMethod, textContent)</code> when calling that function.

blocks|key|2446614|text|首先，考虑用有意义的东西来拒绝，而不仅仅是reject()|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2446615|由于您考虑的是async和promise，我不推荐使用fs.xxxSync()函数。另外，fs.exists已被弃用，请尝试使用fs.stat()。|2446616|我猜只有在HTTP方法是POST的情况下才会创建文件，但是在当前的if-else逻辑中，当HTTP方法不是POST时，总是会创建文件。|2446617|不需要创建立即调用的异步函数。|2446618|试试这个：|2446619|function+createFile(dir,+fileName,+httpMethod,+textContent)+{
++++return+new+Promise((resolve,+reject)+=>+{
++++++++const+searchPath+=+path.join(ROOT_DIR,+dir,+fileName);
++++++++if+(httpMethod+!==+POST)+{
++++++++++++return+reject(new+Error('Invalid+HTTP+method'));
++++++++}
++++++++fs.exists(searchPath,+(exists)+=>+{
++++++++++++if+(exists)+{
++++++++++++++++return+reject(new+Error('Already+exists'));
++++++++++++}
++++++++++++fs.exists(path.join(ROOT_DIR,+dir),+async+(exists)+=>+{
++++++++++++++++try+{
++++++++++++++++++++if+(!exists)+{
++++++++++++++++++++++++await+mkDirPromise(dir);
++++++++++++++++++++}
++++++++++++++++++++await+writeFilePromise(searchPath,+textContent);
++++++++++++++++++++resolve();
++++++++++++++++}+catch+(err)+{
++++++++++++++++++++reject(err);
++++++++++++++++}
++++++++++++});
++++++++});
++++});
}|code-block|syntax|javascript|2446620|entityMap^0|L|8|0|R|C|19|9|1S|9|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|15|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|16|8|@]|D|@]|E|$]]|$1|N|3|O|5|P|7|17|8|@]|D|@]|E|$Q|R]]|$1|S|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|T|$]]

First, consider rejecting with something meaningful instead of just <code>reject()</code>

Since you are thinking with async and promise, I don't recommend using <code>fs.xxxSync()</code> functions. Also, <code>fs.exists</code> is deprecated, try using <code>fs.stat()</code>.

I guess you will only create the file if the HTTP method is POST, but the file will always be created when HTTP method is not POST in the current if-else logic.

It is unnecessary to create an immediately-invoked async function.

Try this:

<pre><code>function createFile(dir, fileName, httpMethod, textContent) {
 return new Promise((resolve, reject) =&gt; {
 const searchPath = path.join(ROOT_DIR, dir, fileName);
 if (httpMethod !== POST) {
 return reject(new Error('Invalid HTTP method'));
 }
 fs.exists(searchPath, (exists) =&gt; {
 if (exists) {
 return reject(new Error('Already exists'));
 }
 fs.exists(path.join(ROOT_DIR, dir), async (exists) =&gt; {
 try {
 if (!exists) {
 await mkDirPromise(dir);
 }
 await writeFilePromise(searchPath, textContent);
 resolve();
 } catch (err) {
 reject(err);
 }
 });
 });
 });
}
</code></pre>

I'm writing a function <code>createFile</code> to create a file in a directory unless it already exists. I'm using Node.js native <code>fs</code> package to do all file operations. I wanted to make my function asynchronous so I wrapped all <code>fs</code> functions in promises:

<pre><code>function writeFilePromise(writePath, textContent) {
 return new Promise((resolve, reject) =&gt; {
 fs.writeFile(writePath, textContent, (err) =&gt; {
 reject();
 });
 resolve();
 });
 }

 function mkDirPromise(dir) {
 return new Promise(((resolve, reject) =&gt; {
 fs.mkdir(path.join(constants.FILES_STORAGE_DIR, dir), (err) =&gt; {
 reject(err);
 });
 resolve();
 }));
 }
</code></pre>

Then I wanted to also wrap <code>fs.existsSync</code> in promise in order to complete my function but wrapping it resulted in occasional incorrect behavior, namely, if a directory for the file didn't exist and I wanted to create one the directory would be created empty without the file. Through debugging I found that only synchronous <code>fs.existsSync</code> would work always.
This the function code:

<pre><code>function createFile(dir, fileName, httpMethod, textContent) {
 return new Promise(((resolve, reject) =&gt; {
 const searchPath = path.join(ROOT_DIR, dir, fileName);
 if (httpMethod === POST &amp;&amp; fs.existsSync(searchPath)) {
 reject();
 } else {
 const fileExistsStatus = fs.existsSync(path.join(ROOT_DIR, dir));
 (async function fsOperations() {
 try {
 if (!fileExistsStatus) {
 await mkDirPromise(dir);
 }
 await writeFilePromise(searchPath, textContent);
 resolve();
 } catch (err) {
 reject(err);
 }
 }());
 }
 }));
 }
</code></pre>

What am I missing and how can I turn my function into truly asynchronous?

Why node.js `fs.existsSync` doesn't work well when wrapped in promise?

我正在编写一个函数createFile，用于在一个目录中创建一个文件，除非该文件已经存在。我使用Node.js原生fs包来执行所有文件操作。我想让我的函数异步，所以我把所有的fs函数都包装在promises中：function writeFilePromise(writePath, textContent) {    ...

问为什么node.js `fs.existsSync`在promise中不能很好地工作？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问为什么node.js `fs.existsSync`在promise中不能很好地工作？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问为什么node.js `fs.existsSync`在promise中不能很好地工作？
EN