Understanding Promises

What is a Promise?

A Promise is an object representing the eventual completion or failure of an asynchronous operation.

A Promise is in one of these states:

• pending: initial state, neither fulfilled nor rejected.
• fulfilled: meaning that the operation was completed successfully.
• rejected: meaning that the operation failed.

Creating Promises

You create a Promise using the Promise constructor which takes a function (executor) with two parameters: resolve and reject.

const myPromise = new Promise((resolve, reject) => {
  // Asynchronous operation
  if (/* operation successful */) {
    resolve(result); // fulfilled with result value
  } else {
    reject(error);   // rejected with error reason
  }
});

Promise Chaining

Promises can be chained together using .then() methods, allowing you to sequence asynchronous operations.

fetchData()
  .then(data => processData(data))
  .then(processedData => displayData(processedData))
  .catch(error => handleError(error));

Error Handling with Promises

Promises provide a clean way to handle errors using .catch() method.

Promise.all & Promise.race

Promise.all() waits for all promises to resolve, while Promise.race() returns as soon as one promise resolves or rejects.