DeprecationWarning: Calling an asynchronous function without callback is deprecated. in fs.writeFile

[thidasapankaja]

Version: v8.0.0
Platform: Linux pankaja-HP-Pavilion-15-Notebook-PC 4.10.0-30-generic #34~16.04.1-Ubuntu SMP Wed Aug 2 02:13:56 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
Subsystem: fs.writeFile

Error : (node:10801) [DEP0013] DeprecationWarning: Calling an asynchronous function without callback is deprecated.

Code :

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

var server = http.createServer(function(req, res){

	fs.readFile("text.txt",'utf-8',function(error, data){
		res.writeHead(200,{
			'Content-Type': 'tex/plain'
		});

		data = parseInt(data) + 1;

		fs.writeFile("text.txt", data);

		res.end('This page was refreshed ' + data + ' times!');
	})
});

server.listen(8080, function(){
	console.log('your server is running at 127.0.0.1:8080')
})

I was following this tutorial and when Reading and Writing files I'm getting this error. When I use node --trace-deprecation file.js I'm getting this log message.

(node:10880) [DEP0013] DeprecationWarning: Calling an asynchronous function without callback is deprecated.
at maybeCallback (fs.js:119:42)
at Object.fs.writeFile (fs.js:1256:14)
at /media/pankaja/Local Disk/Projects/Nodejs/Tutorial/file.js:14:6
at tryToString (fs.js:499:3)
at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:487:12)

Is this a bug ?

[vsemozhetbyt]

Hi, @pankaja92. The tutorial is a bit outdated (5 years old) in that fs asynchronous functions now demand a callback. You can fix your code by updating this line:

fs.writeFile("text.txt", data);

by this one:

fs.writeFile("text.txt", data, (error) => { /* handle error */ });

see https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback

[tommedema]

@vsemozhetbyt but why use a callback when one can use async/await with try catch?

[TimothyGu]

@tommedema Node.js fs module functions do not return a promise, and cannot be used with async/await try-catch by default. You can convert the functions to become promise-returning though with the use of util.promisify.

[jacobq]

Alternatively, if you want to use promises / async functions you can use fs-extra like this.

[quyle1710]

@vsemozhetbyt Thank you for this answer :)

[jasnell]

Starting in Node.js 10.0.0, there are experimental promise versions of the fs functions available at fs.promises

[flyher]

@vsemozhetbyt
Thank you for the answer!

[Sai0407]

Can any one help me imagemin
(node:13696) [DEP0013] DeprecationWarning: Calling an asynchronous function without callback is deprecated.

[cloudemp04]

i also have the same problem heres my gulpfile code

'use strict';

var gulp = require('gulp');
var concat = require('gulp-concat');
var merge = require('merge-stream');
var browserSync = require('browser-sync').create();
var sass = require('gulp-sass');
var plumber = require('gulp-plumber');
var uglify = require('gulp-uglify');

// Static Server + watching scss/html files
gulp.task('serve', ['sass','js'], function() {

browserSync.init({
	server: "."
});

gulp.watch([
		   "assets/scss/utils/*.scss",
		   "assets/scss/components/*.scss",
		   "assets/scss/base/*.scss",
		   "assets/scss/layouts/*.scss",
		   'assets/gulp-js/*.js'
		   ], ['sass','js']);
gulp.watch("*.html").on('change', browserSync.reload);

});

// Compile sass into CSS & auto-inject into browsers
gulp.task('sass', function() {
return gulp.src([
"assets/scss/utils/.scss",
"assets/scss/components/.scss",
"assets/scss/base/.scss",
"assets/scss/layouts/.scss"
])
.pipe(concat('assets/css/style.css'))
.pipe(plumber({
handleError: function(err) {
console.log(err);
this.emit('end');
}
}))
.pipe(sass({outputStyle : 'compressed'}))
.pipe(gulp.dest("./"))
.pipe(browserSync.stream());
});

gulp.task('js', function() {
return gulp.src('assets/gulp-js/*.js')
.pipe(concat("index.js"))
.pipe(uglify())
.pipe(gulp.dest('assets/js/'))
.pipe(browserSync.stream());
});

gulp.task('default', ['serve']);

anyone can help me?

[joyeecheung]

If you encounter a deprecation warning but do not know what code causes it (usually because it's code in your dependency), you can use the --trace-warnings command line flag to see the stack trace and find out which line of code is using a deprecated API. If it's in your dependency, try either upgrading it or opening a PR for them.