Writing a File in Node.js

In the post Reading a File in Node.js we saw how to use methods of fs module to read a file. In this post we'll see how to write a file in Node.js using the methods of the fs module.

How to write to a file in Node.js

In the fs module there are two methods to write to a file.

fs.writeFile()- This functions writes the file content in a non-blocking, asynchronous manner, replacing the file if it already exists. A callback function is provided which is called when the file write operation is completed.

fs.writeFileSync()- It is the synchronous function for writing content to a file which means it blocks while the write operation is in progress. The function returns undefined.

Apart from these two methods there is also a writeFile() function in the fs.promises API which asynchronously writes to a file and returns a Promise object which is resolved with no arguments upon success. Thus, you don't need a callback function.

Using fs.writeFile()

Syntax of fs.writeFile() method is as given below.

fs.writeFile( file, data, options, callback )

The four parameters are described below-

1. file- Path to the file where content has to be written or file descriptor (a number returned by opening the file using the open() method).
2. data- Content to be written to the file. It can be of type string, Buffer, TypedArray, DataView.
3. options- It specifies optional parameters that can be provided with write operation. Type can be either string or object. Optional parameters are described below-
   • encoding- A string value specifying the encoding of the file. Default is 'utf8'
   • mode- An integer value specifying the file mode. Default is 0o666 which means both read and write.
   • flag- Flag used in write operation. Default flag is 'w' which means open file for writing, file is created if it doesn't exist or truncated if it exists.
   • flush- If all data is successfully written to the file, and flush is true, fs.fsync() is used to flush the data. Default value is false.
   • signal- Allows aborting an in-progress writeFile
4. callback- A function that is called when the file operation completes. Takes one argument err which denotes the error that can be thrown if write operation fails.

fs.writeFile () Example

const fs = require('fs');
const path = require('path');

const content = 'Hello World from NodeJS!!';

fs.writeFile(path.join(__dirname, 'Hello.txt'), content, (err)=>{
    if(err){
        console.error('Error while writing to a file', err);
        return;
    }
});

If you want to give optional parameters then you can pass them as shown below-

const fs = require('fs');
const path = require('path');

const content = 'Hello World from NodeJS!!';

fs.writeFile(path.join(__dirname, 'Hello.txt'), content,  {
    encoding: "utf8",
    flag: "w",
    mode: 0o666
  }, (err)=>{
    if(err){
        console.error('Error while writing to a file', err);
        return;
    }
    console.log('File written Successfully');
});

Using fs.writeFileSync()

Syntax of fs.writeFileSync() method is as given below

fs.writeFileSync(file, data, options)

Description of parameters is similar to fs.writeFile()

fs.writeFileSync() Example

const fs = require('fs');
const path = require('path');

const content = 'Hello World from NodeJS!!';

try {
    fs.writeFileSync(path.join(__dirname, 'Hello.txt'), content);
    console.log('File written Successfully');
} catch (err) {
    console.error(err);
}

Using fsPromises.WriteFile()

Syntax of fsPromises.writeFile() method is as given below.

fsPromises.writeFile(file, data, options)

Description of parameters is similar to fs.writeFile() method as given above.

fsPromises.WriteFile() Example

const fs = require('fs');
const fsPromises = fs.promises;
const path = require('path');

async function writeFile(filePath) {
    try {
        const content = 'Hello World from NodeJS';
        await fsPromises.writeFile(filePath, content);
    } catch (err) {
        console.log(err);
    }
}

That's all for this topic Writing a File in Node.js. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Related Topics

1. Appending a File in Node.js
2. NodeJS Blocking Non-blocking Code
3. Node.js REPL
4. NodeJS NPM Package Manager
5. Creating HTTP server in Node.js

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