Print the information when the change occurs and take a look
See what operations the editor performs on the file. Accessing/modifying the file will trigger the file change event
Node writes the file and then monitors the file. Nothing appears as you said The problem is as follows:

var fs = require('fs');
var util=require('util');

fs.watch('./test.log', {}, function(e){
    var stats = fs.statSync('./test.log');
    console.log(util.inspect(stats));//打印发生变化时的信息
    console.log(stats.size)
});

var writeStream=fs.createWriteStream('./test.log', {
    flags: 'a+',
    defaultEncoding: 'utf8'
});

setInterval(function(){
    writeStream.write("a");
},1000);

I haven’t tried it, it’s probably because the file was occupied when you were adding text,

Just ctrl+s will be executed twice