Javascript File Handling: 11 Golden Rules to Follow as a Programmer

As software applications become increasingly complex, file handling has become a significant challenge for developers. In light of this, I have taken it upon myself to address this problem by creating a simple yet insightful post that will help developers understand the ins and outs of file handling in JavaScript.

11 Best Practices for Javascript File Handling

1. Always handle errors: When dealing with files, errors are inevitable. Ensure that errors are handled gracefully and meaningful error messages are displayed to the users.

   Example:

const file = new File(['Hello, world!'], 'hello.txt', {type: 'text/plain'});
const reader = new FileReader();

reader.onerror = (event) => {
  console.error(`Error occurred while reading file: ${event.target.error}`);
};

reader.readAsText(file);

2. Use appropriate file types: Always validate file types before accepting file uploads from users to prevent malicious or invalid files from being uploaded.

   Example:

const fileInput = document.getElementById('file-input');
const allowedFileTypes = ['image/jpeg', 'image/png', 'application/pdf'];

fileInput.addEventListener('change', (event) => {
  const file = event.target.files[0];
  if (!allowedFileTypes.includes(file.type)) {
    alert('Invalid file type. Please upload a JPEG, PNG, or PDF file.');
    event.target.value = null;
  } else {
    // Handle file upload
  }
});

3. Close file streams when done: If you are reading or writing files, close the file stream when you are done to free up system resources.

   Example:

const file = new File(['Hello, world!'], 'hello.txt', {type: 'text/plain'});
const writer = new FileWriter();

writer.write(file);

// Close file stream when done
writer.close();

4. Use asynchronous methods: I/O operations on files can be time-consuming and block the main thread. In order to avoid freezing the UI and improve performance, always use asynchronous methods.

   Example:

const file = new File(['Hello, world!'], 'hello.txt', {type: 'text/plain'});

async function readFile() {
  const reader = new FileReader();
  return new Promise((resolve, reject) => {
    reader.onload = (event) => resolve(event.target.result);
    reader.onerror = (event) => reject(event.target.error);
    reader.readAsText(file);
  });
}

readFile()
  .then((content) => console.log(content))
  .catch((error) => console.error(error));

5. Be mindful of file size: It is important to keep in mind the performance impact of large files on an end user's device when working with them. Use streaming techniques to load the file into memory in small chunks rather than loading it all at once.

   Example:

const file = new File(['Hello, world!'.repeat(1000000)], 'hello.txt', {type: 'text/plain'});

function processFile() {
  const stream = file.stream();
  const reader = stream.getReader();

  function readChunk() {
    return reader.read()
      .then(({value, done}) => {
        if (done) {
          console.log('Finished processing file');
          return;
        }
        console.log(`Read chunk of size ${value.byteLength}`);
        return readChunk();
      });
  }

  return readChunk();
}

processFile();

6. Use descriptive file names: Choose file names that accurately reflect the contents and purposes of the files. A file containing utility functions, for example, could be named utils.js.

7. Use modular design: Organize your code into modular components to make it easier to understand and maintain. The use of modules allows you to organize related code and reduce the chance of naming conflicts.

8. Use strict mode: Adding use strict to your JavaScript file will enforce stricter syntax rules, catch common errors, and improve performance.

9. Use comments: Describe the purpose, behavior, and limitations of your code in the comments. You will be able to make your code more understandable to other developers and to yourself in the future.

10. Use linting tools: You can use a linter to find and correct syntax errors, style issues, and potential bugs. Linting tools such as JSLint, ESLint, and JSHint are widely used.

11. Use version control: Track changes to your code and collaborate with other developers with a version control system like Git. In this way, you can avoid version conflicts and revert to previous versions of your code if necessary.

The following JavaScript file implements some of these best practices:

'use strict';

// This module contains utility functions.

// Returns the sum of two numbers.
function add(num1, num2) {
  return num1 + num2;
}

// Returns the difference between two numbers.
function subtract(num1, num2) {
  return num1 - num2;
}

// Exports the functions for use in other modules.
module.exports = {
  add: add,
  subtract: subtract
};

In this example, utils.js indicates that it contains utility functions. Each function is defined separately in the code, which is broken into modular components. The use strict directive enforces stricter syntax rules. Comments are used to explain the purpose of each function. Finally, the functions are exported for use in other modules using the module.exports object.

Wrap-up

File handling in JavaScript is an important skill for any programmer. By following the 11 golden rules outlined in this article, programmers can ensure that they are creating robust and efficient code that is easy to maintain and debug. With a solid understanding of these best practices, developers can take their file-handling capabilities to the next level and create truly exceptional applications.

These are just a few examples of JavaScript file-handling best practices. Also, be sure to follow web application security best practices when working with user-generated files.