3-Node-FileSystem.md

INDEX

• INDEX
  • Asynchronous node.js and Callbacks
    • callbacks
  • File System vs Database
  • Using File System to Open and Write Files
    • File System Flags
    • Reading and Writing with File System
    • Reading, Moving, Renaming and Deleting Files
  • Streams
    • Pipe

---

Asynchronous node.js and Callbacks

• Node.js introduced a non-blocking I/O environment to extend this concept to file access, network calls and so on.

callbacks

• we use callbacks a lot in node as we deal with events, requests, .. and we don't know when they will be executed

• to escape from callback-hell we use Promises or Async/Await

• instead use __dirname in template-literals which indicate the place where the js file exists ->

  const tempOverview = fs.readFileSync(`${__dirname}/templates/template-overview.html`, 'utf-8');

• To avoid using callbacks, we can use the File System Promises API which allows the asynchronous methods to return promises.

  import {promises as fsPromises} from fs;
  // or
  import {promises as fs} from fs;

---

File System vs Database

• databases are just files.

  • With Databases the content is structured, can be relational, and indexed.

• With File System, you can only control where you write to the file, and where you read from the file

  • so File System is only good for simple data storage.

---

Using File System to Open and Write Files

File System Flags

File System Flags are used for identifying read/write operations available when opening a file.

---

Reading and Writing with File System

• .open() - Used to open a file. Takes a filename and flag as arguments.

  const writeData = async () => {
  const myFile = await fsPromises.open('myfile.txt', a+);
  }

• .write() / .writeFile() Takes data, and options as arguments.

• 

  const writeData = async () => {
    const myFile = await fsPromises.open('myfile.txt', a+);
    await myFile.write('add text');
  }
  
  // or
  
  const writeData = async () => {
  const myFile = await fsPromises.writeFile('myfile.txt', 'The added text');
  }

---

Reading, Moving, Renaming and Deleting Files

• .read() - Used to read a file. The file must be opened first. requires the creation of a buffer to do so. Takes a buffer and options as arguments.

  const readData = async () => {
    const buff = new Buffer.alloc(26);  // 26 characters max
    const myFile = await fsPromises.open('myfile.txt', a+);
    await myFile.read(buff, 0, 26);
    console.log(myFile);
  }

• .readFile() - Used to read the entire contents of a file. Takes a path and options as arguments.

  const readData = async () => {
    const myFile = await fsPromises.readFile('myfile.txt', 'utf-8');
    console.log(myFile);
  };

• .rename() - Used to rename or move a file. Takes the old file path and new file path as arguments.

• .mkdir() - Used to make new directories. Takes a directory path as an argument.

• .unlink() - Used to remove a file. Takes a file path as an argument.

• .rmdir() - Used to remove an empty directory. Takes a directory path as an argument.

• For removing directories that contain files without needing to remove the files first, it's easiest to use a third-party module such as rimraf

---

Streams

• it's a good idea to stream large datasets so that they don't overwhelm te (cpu, Ram,..)
• to read streams we use the File System (fs) : it emmits a event called 'data'

fs.createReadStream('kepler_data.csv').on('data', data => {
  console.log(data);
});

Pipe

• It connects stream source with stream distination
• in the pipe, we put the thing that deal with incoming data in the start of the pipe, ex : parsing data functionality

fs.createReadStream('kepler_data.csv')
  .pipe(parser) // do parsing on incoming data
  .on('data', data => {
    console.log(data);
  });