The promisify-if-no-callback package is a utility that converts Node.js-style callback functions into Promise-based functions when no callback is provided, allowing you to work with asynchronous operations using either traditional callbacks or modern Promise-based syntax.

You can install the promisify-if-no-callback package via NPM:

npm install promisify-if-no-callback

To use the promisify-if-no-callback function, require it in your Node.js application:

const promisifyIfNoCallback = require('promisify-if-no-callback');

const promisifiedFunction = promisifyIfNoCallback(originalFunction);

• originalFunction (Function): The function you want to promisify. It should follow the Node.js-style callback pattern where the last argument is a callback function (function (err, result) {}).

The promisify-if-no-callback function returns a new function that can be used with Promises. When you call this new function, it either behaves like the original function with a callback or returns a Promise, depending on how you invoke it.

If you pass a callback as the last argument, the function will behave as the original function, allowing you to use callbacks for handling results.

If you don't pass a callback, the promisify-if-no-callback function returns a Promise that resolves with the result when the asynchronous operation completes successfully or rejects with an error if the operation encounters an error.

const fs = require('fs');
const promisifyIfNoCallback = require('promisify-if-no-callback');

// Promisify the fs.readFile function
const readFilePromise = promisifyIfNoCallback(fs.readFile);

// Use the Promise-based function
readFilePromise('file.txt', 'utf8')
  .then(data => {
    console.log('File contents:', data);
  })
  .catch(err => {
    console.error('Error reading file:', err);
  });

// Assume you have an asynchronous function with a callback
function asyncFunctionWithCallback(param1, param2, callback) {
  // Some asynchronous operation
  setTimeout(() => {
    const result = param1 + param2;
    callback(null, result); // Pass null as the first argument if there's no error
  }, 1000);
}

// Use promisifyIfNoCallback to convert the function to a Promise-based function
const asyncFunctionPromise = promisifyIfNoCallback(asyncFunctionWithCallback);

// Using the original callback-style invocation
asyncFunctionWithCallback(2, 3, (err, result) => {
  if (err) {
    console.error('Error:', err);
  } else {
    console.log('Result (callback):', result);
  }
});

This project is licensed under the ISC License.

If you encounter any problems or have questions about the library, please feel free to open an issue on the GitHub repository.