Write to file without callback Node js

Question

How do you write a writeFile() function without a callback?

This does not work:

fs.writeFile("/logs/file.log", 'Message')

fs.writeFile("/logs/file.log", 'Message',null)

Both throw a:

TypeError [ERR_INVALID_CALLBACK]: Callback must be a function

I need to implement a non-blocking solution.

Answer 1

// create a noop - as in "no operation"
const noop = () => {};

// and pass that in
fs.writeFile("filename.txt", "content", noop);

If you're bothered by having to pass a callback at all, create another function:

const writeFile = (filename, content) => {fs.writeFile(filename, content, () => {}));

// and use it like this
writeFile("filename.txt", "content");

Better yet, if you're using NodeJS > v10.0, then use the fs.promises.writeFile API:

import fs from "fs";

// this returns a Promise
fs.promises.writeFile("filename.txt", "content");

// which you can await in an async function
async main() {
    try {
        await fs.promises.writeFile("filename.txt", "content");
    }
    catch (e) {
        console.error(e);
    }
}

// or .then and .catch on it.
fs.promises.writeFile("filename.txt", "content")
    .then(() => { /* do something after */ })
    .catch(e => console.error(e));

If on Node < v10.0 you can use the promisify utility:

import { promisify } from "util";
import fs from "fs";

const writeFile = promisify(fs.writeFile);

// this returns a Promise that you can await or .then
await writeFile("filename.txt", "content");

Answer 2

I need to implement a non-blocking solution.

Because of that you must use an ASYNC function instead of sync.

writefile() is an async function, thus you need a callback function for it.

var fs = require('fs');
fs.writeFile("/logs/file.log", "Message", function(err) {
    if(err) {
        return console.log(err);
    }

    console.log("The file is saved!");
    // Here you can write code about what happen next!

}); 

Answer 3

If you really don't care about the result (error yes/no), this might do the trick.

fs.writeFile("/logs/file.log", 'Message', () => {})

Answer 4

Instead of using writeFile, you can use writeFileSync instead. writeFile requires the callback to be passed whereas writeFileSync doesn't need a callback function. For more info, you can refer to writeFileSync NodeJS Docs

This should work for you

fs.writeFileSync("/logs/file.log", 'Message')

As I read your comment on the question, if you are looking to stick to writeFile, you need to pass the callback function as it's async. You can shorten it by writing

fs.writeFile("/logs/file.log", 'Message', () => {})