promisifyAll

promisifyAll is a utility function commonly found in JavaScript libraries, most notably in the Bluebird Promise library. Its primary purpose is to convert an object's methods that traditionally use callback patterns into methods that return Promises. This simplifies asynchronous code by allowing developers to use the more modern and readable Promise syntax instead of nested callbacks.

When promisifyAll is applied to an object, it iterates through the object's properties. If a property is a function and follows a standard Node.js-style callback convention (where the last argument is a callback function that receives an error as its first argument and a result as its second), promisifyAll will create a new function for that property. This new function will return a Promise. When the original callback-style function is invoked and its callback is eventually called, the Promise will either resolve with the result or reject with the error.

For example, if you have an object with a method like `fs.readFile(path, encoding, callback)`, promisifyAll would transform it so you could call `fs.readFileAsync(path, encoding)` which would return a Promise. This allows for cleaner chaining of asynchronous operations using .then() and .catch() or async/await syntax. It's a convenient way to bridge older callback-based APIs with modern Promise-based JavaScript.