Promisify with Recursion

What is Promisify?

In JavaScript, promisify refers to converting a function that follows the traditional callback-style asynchronous pattern into a function that returns a Promise.

This is useful when working with legacy APIs or functions that rely on callbacks, as Promises provide a more structured and readable way to handle asynchronous operations.

Implementing Promisify with Recursion

Here, we define an example where a list of Promises is executed recursively, ensuring that each Promise resolves before moving on to the next.

Example: Recursive Promise Execution

const promiseList = [
  new Promise((resolve) => {
    console.log("Promise 1 resolved.");
    resolve("Promise 1 resolved.");
  }),
  new Promise((resolve) => {
    console.log("Promise 2 resolved.");
    resolve("Promise 2 resolved.");
  }),
  new Promise((resolve) => {
    console.log("Promise 3 resolved.");
    resolve("Promise 3 resolved.");
  }),
];
 
function promiseFunc(promiseList, index = 0) {
  if (index >= promiseList.length) {
    console.log("All promises resolved.");
    return Promise.resolve("Done.");
  }
 
  return promiseList[index].then(() => {
    return promiseFunc(promiseList, index + 1);
  });
}
 
promiseFunc(promiseList).then((result) => console.log(result));

Explanation

1. Base Case: If index is greater than or equal to the length of promiseList, the function resolves with "Done." and stops execution.
2. Recursive Case: The function executes the current Promise and then recursively calls itself with the next index.
3. Ensures Sequential Execution: Each Promise waits for the previous one to complete before proceeding.
4. Returns a Promise: The function always returns a Promise, making it chainable.

Why Use Recursion?

• Ensures each asynchronous operation completes before starting the next.
• Eliminates the need for loops with await, keeping the code functional and clean.
• Works well when handling dynamic lists of asynchronous tasks.

By applying promisify with recursion, we can create better control flow for async operations in JavaScript.