Write Files

Write Files

(This is part of a brief series on the fs module)

Writing Files Syncrhonously

The writeFileSync method of the fs module can be used to write files to disk:

const { writeFileSync } = require('fs');
const FILE_TO_WRITE = './../from-writeFileSync.txt';

writeFileSync(FILE_TO_WRITE,'this is a string\n');

Leveraging Flags For More Explicit FInteraction Expectations

Node has a bunch of file system flags that can be used to be more explicit about interaction expectations. Here's a few examples:

ax: Fail When The File Already Exists


// assuming the file already exists
const { writeFileSync } = require('fs');
const FILE_TO_WRITE = './../from-writeFileSync.txt';

writeFileSync(FILE_TO_WRITE, 'this is a string\n', { flag: 'ax' });

// will throw an error:
// Error: EEXIST: file already exists, open './../from-writeFileSync.txt'

a+ Append When The File Already Exists

const { writeFileSync } = require('fs');
const FILE_TO_WRITE = './../from-writeFileSync.txt';

writeFileSync(FILE_TO_WRITE, 'this is a string\n', { flag: 'a+' });

Keeping The Event Loop Open with writeFile

const { writeFile } = require('fs');
const FILE_TO_WRITE = './../from-writeFile.txt';

function writeFileCallback(err) {
  if (err) {
    console.error(err);
    return;
  }
  console.log('done writing');
}

writeFile(FILE_TO_WRITE, 'this is a string\n', writeFileCallback);

Keeping The Event Loop Open with The Promise API

the node fs module has a nice built-in promise-syntax api:

const { writeFile } = require('fs/promises');
const FILE_TO_WRITE = './../new-file.txt';

writeFile(FILE_TO_WRITE, 'this is a string\n').then(() => { 
  console.log('done writing!')
}).catch(console.log);

Tags:

node

core

event loop