javascript - Difference between readFileSync and using promisify on top of readFile with asyncawait - Stack Overflow

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Out of curiosity, i want to know if there is any difference between the two.

readFileSync:

function parseFile(filePath) {
  let data = fs.readFileSync(filePath);
}

Out of curiosity, i want to know if there is any difference between the two.

readFileSync:

function parseFile(filePath) {
  let data = fs.readFileSync(filePath);
}

readFile with promisify:

const readFilePromise = promisify(fs.readFile);
async function parseFile(filePath) {
  let data = await readFilePromise(filePath);
}

If you need some context, im trying to read a bunch of files in a folder, replace a lot of values in each one, and write it again.

I don`t know if there is any difference in using Asyncronous or Synchronous code for these actions.

Full code:

function parseFile(filePath) {
  let data = fs.readFileSync(filePath);
  let originalData = data.toString();
  let newData = replaceAll(originalData);

  return fs.writeFileSync(filePath, newData);
}

function readFiles(dirPath) {
  let dir = path.join(__dirname, dirPath);
  let files = fs.readdirSync(dir); // gives all the files
  files.map(file => parseFile(path.join(dir, file)));
}

function replaceAll(text) {
  text = text.replace(/a/g, 'b');
  return text;
}

readFiles('/files');

• javascript
• node.js
• async-await
• fs

Share Improve this question Follow edited Dec 11, 2018 at 18:00 Patrick Passarella asked Dec 11, 2018 at 17:47 Patrick PassarellaPatrick Passarella 18311 silver badge77 bronze badges 4

• Why it got downvoted..? Even the answer – Patrick Passarella Commented Dec 11, 2018 at 18:33
• 4 Not sure about the dv. I think it's pretty rude to downvote with no ment. Especially new contributors. I'll pass on an upvote to help. – Mark Commented Dec 11, 2018 at 18:35
• This question is extremely broad and is likely the cause of a downvote (speculation). Synchronous code executes in a single stack frame, asynchronous code is relinquished to the event queue. You should understand how the stack and event loop work together to understand the difference between synchronous and asynchronous code execution in javascript. I generally remend watching this video to understand these concepts. – Jake Holzinger Commented Dec 11, 2018 at 21:10
• But i actually know how async vs sync works, i wanted to know the difference especifically between these 2 fs methods, if there was any difference. – Patrick Passarella Commented Dec 12, 2018 at 15:34

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 12

There's a big difference between the async and synchronous code. Whether that difference matters depends on what you are trying to do. Your javascript is singe threaded, so while you are reading a potentially large file synchronously with fs.readFileSync you can't do anything else such as respond to ining requests.

If you are running a busy server this can cause big problems because requests queue up while you are reading the file and you may never catch up.

With the async method the file read happens outside your code and it calls your code back when it's done. While it's doing this your code is free to respond to other requests.

If you are just trying to read a local file and it doesn't matter if the thread blocks, then you can use either.

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