3. Reading and Writing Files in Node.js

• Node.js provides the fs (File System) module to interact with the file system for reading and writing files.
• It includes both asynchronous and synchronous methods for working with files

Reading Files

• Synchronous File Reading
  • readFileSync is the synchronous method for reading files, it only takes the file location and the file encoding
  • This will block code execution until the file has been read
  • In applications where performance is critical, it’s often preferred to use the asynchronous version, but the synchronous version can be a lot easier to reason about
  • Example

    const data = fs.readFileSync('example.txt', 'utf8');
    console.log(data);
    • This will block the code until the entire contents of example.txt are read, and then print out the contents.
• Asynchronous File Reading
  • readFile is the asynchronous method for reading files, it take the file location and encoding, same as the synchronous method. However, it also takes a callback function which will be ran after the file contents are read
  • The callback function takes two parameters when it is ran, an Error object (in case an error occurs while reading) and a string containing the file contents
  • Example

  fs.readFile('example.txt', 'utf8', (err, data) => {
    if (err) {
      console.error(err);
      return;
    }
    console.log(data);
  });
  • This will not block the code, but when the reading of example.txt has finished, the data will be printed or the error (if applicable)

Writing Files

• Synchronous File Writing
  • writeFileSync (like readFileSync) is the synchronous method for writing files
  • Again, it will block execution until the file has been written and it is often preferred to use the asynchronous version if performance is an issue
• Asynchronous File Writing
  • Simular to readFile the asyncrhonous counterpart for writing is writeFile
  • writeFile also takes a callback function (like it’s readFile counterpart), however this callback only takes an error parameter, as there is no data to return

Common Errors

• When working with files, there are many opportunities for error
• It’s important to be aware of this, and do your best to handle at least some of the common errors
• File not found: An extremely common error that occurs when the file attemtping to be read, or written to, does not exist.
  • Surrounding any particular code in a try/catch block can help
  • You can also check if a file exists with something like existsSync
• Inadequate permssions: Another common errors that occurs when you don’t have the proper permissions to perform the asked file operation
  • The best method for this error is to use standard error handling like a try/catch statement or checking the error object in the async callback