Understanding Promises in JavaScript

Handling Asynchronous Operations the Right Way

JavaScript is single-threaded, but it can handle asynchronous operations like API calls, file reading, and timers.
To manage these async tasks efficiently, JavaScript provides Promises.

🔹 What is a Promise in JavaScript?

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

In simple words:
👉 “I promise to return a value later — either success or error.”

🔹 Why Do We Need Promises?

Before Promises, JavaScript used callbacks, which caused problems like:

❌ Callback Hell
❌ Hard-to-read code
❌ Difficult error handling

Promises solve these problems by providing:

• Cleaner syntax
• Better error handling
• Chainable operations

🔹 Promise States

A Promise can be in one of three states:

• Pending – Initial state (waiting)
• *Fulfilled *– Operation completed successfully
• Rejected – Operation failed

Once a promise is fulfilled or rejected, it is settled and cannot change again.

🔹 Creating a Promise

`const myPromise = new Promise((resolve, reject) => {
let success = true;

if (success) {
resolve("Promise resolved successfully");
} else {
reject("Promise rejected");
}
});

• resolve() → success result
• reject() → error result`

🔹 Consuming a Promise

`Using .then() and .catch()
myPromise
.then(result => {
console.log(result);
})
.catch(error => {
console.log(error);
});

• .then() → handles success
• .catch() → handles error`

🔹 Promise Chaining

Promises can be chained to **perform multiple async tasks **sequentially.

fetchData()
.then(data => processData(data))
.then(result => displayResult(result))
.catch(error => console.log(error));

✅ Avoids callback hell
✅ Improves readability