Detect file content changes from node.js

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?

---

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 comments):

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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