javascript - Detect file content changes from node.js - Stack Overflow

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I have a simple file watcher build with chokidar

require('chokidar').watch('./target.txt', {}).on('all', function(event, path) {
  console.log(event, path);
}).on('ready', function() {
  console.log('ready');
});

It causes change event every time when I re-save file even without changes. Is there a way to make this fire events only if actual content has been changed?

I have a simple file watcher build with chokidar

require('chokidar').watch('./target.txt', {}).on('all', function(event, path) {
  console.log(event, path);
}).on('ready', function() {
  console.log('ready');
});

It causes change event every time when I re-save file even without changes. Is there a way to make this fire events only if actual content has been changed?

• javascript
• node.js
• watch

Share Improve this question Follow asked Oct 22, 2015 at 10:50 just-borisjust-boris 9,78655 gold badges5151 silver badges8787 bronze badges

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1 Answer 1

Sorted by: Reset to default 6

You can use the stats parameter delivered on add and change. This will only work for changes on the size of the file, which should be enough for the vast majority of cases.

   var watchSize = 0;

    require('chokidar').watch('./target.txt', {}).on('all', function(event, path, stats) {  

        if(stats && stats.size != watchSize) {
            watchSize = stats.size;
            console.log(event);
        }
    }).on('ready', function(path, stats) {
      console.log('ready');
    });

If the few remaining situations are indeed relevant for your case and you have no performance concerns, you can use something like this (following the suggestion in the ments):

var crypto   = require("crypto");
var fs       = require("fs");
var chokidar = require("chokidar");

watchFile("./target.txt");

//----------------------------------------------------
function watchFile(filePath){

    var watchHash;

    chokidar.watch(filePath, {}).on("all", function(event, path, stats) {

        if (event == "add" || event == "change"){

            getHash(filePath, function(hash){
                if (hash != watchHash){
                    watchHash = hash;
                    console.log(event);
                }
            });
        }
    });
}

//----------------------------------------------------
function getHash(filePath, callback){

    var stream = fs.ReadStream(filePath);   
    var md5sum = crypto.createHash("md5");

    stream.on("data", function(data) {
        md5sum.update(data);
    });

    stream.on("end", function() {
        callback(md5sum.digest("hex"));
    });
}

This seems a bit much, though.

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