JavaScript Promises

A Promise is a JavaScript object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value.

⏳ Why Promises?

• Improve readability of async code
• Avoid "callback hell"
• Easy error handling with .catch()

📄 Basic Syntax

const promise = new Promise((resolve, reject) => {
    const success = true;

    if (success) {
        resolve("✅ Operation successful");
    } else {
        reject("❌ Something went wrong");
    }
});

promise
    .then(result => console.log(result))
    .catch(error => console.error(error));

💡 Example: Simulate API

function fetchData() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve("📦 Data received");
        }, 2000);
    });
}

fetchData()
    .then(data => console.log(data))
    .catch(err => console.error(err));

🔁 Chaining Promises

fetchData()
    .then(data => {
        console.log(data);
        return "🔍 Processing data";
    })
    .then(processed => console.log(processed))
    .catch(err => console.error(err));

📦 Promise States

• Pending: Initial state
• Fulfilled: Operation completed
• Rejected: Operation failed