Strange behavior with `fs.watch` on file with JSON stringified -> first update isn't emitted if too fast after `fs.watch`
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- JavaScript
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Description
Node.js Version
v18.17.1
NPM Version
9.6.7
Operating System
23.2.0 Darwin
Subsystem
fs
Description
I would like to watch changes on a file storing JSON stringified data but the watcher created with fs.watch is not emitted if the change happen to quickly after the call of fs.watch. The strange thing is that if the content is only a text (without JSON format) the watcher emit the event correctly...
Minimal Reproduction
const fs = require('fs');
const path = require('path');
const filePath = path.join(__dirname, 'test.json');
// Create the file if it doesn't exist
if (!fs.existsSync(filePath)) {
fs.writeFileSync(filePath, "{ }");
}
fs.watch(filePath, (eventType, filename) => {
console.log(`Event type is: ${eventType}`);
if (filename) {
console.log(`Filename provided: ${filename}`);
} else {
console.log('Filename not provided');
}
});
fs.writeFileSync(filePath, "{ \"test\": \"test\", \"test2\": \"test2\" }"); // same with JSON.stringify(...)
// Listener above is called if we replace line above with:
// fs.writeFileSync(filePath, "very ok or not but I need a longer text to test something...");
Output
Expected
Event type is: change
Filename provided: test.json
Received
Nothing
Before You Submit
- I have looked for issues that already exist before submitting this
- My issue follows the guidelines in the README file, and follows the 'How to ask a good question' guide at https://stackoverflow.com/help/how-to-ask
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the minimal reproduction using fs.watch and the immediate fs.writeFileSync call on Darwin. Compare the JSON-stringified write with the longer plain-text write and investigate the first-event timing behavior. Done means the expected change event is reliably emitted for the JSON write without breaking the documented fs.watch behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript, node.js
- Domain
- operating-systems
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100