JavaScript Promises – Introduction

JavaScript Promises – Introduction

Promise in JavaScript is an object that represents the result of an asynchronous operation (something that takes time, like fetching data).

A Promise can be in 3 states:

Pending – operation is still running

Fulfilled – operation completed successfully

Rejected – operation failed

Why Promises?**

Before promises, JavaScript used callbacks, which caused callback hell (messy nested code).
Promises make async code clean, readable, and manageable.

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

if (success) {
resolve("Task completed");
} else {
reject("Task failed");
}
});

Consuming a Promise
myPromise
.then((result) => {
console.log(result); // Task completed
})
.catch((error) => {
console.log(error); // Task failed
});

Promise Example (Real-life style)
function orderFood() {
return new Promise((resolve, reject) => {
let foodReady = true;

if (foodReady) {
  resolve("Food delivered 🍔");
} else {
  reject("Order cancelled ❌");
}

});
}

orderFood()
.then(msg => console.log(msg))
.catch(err => console.log(err));

Promise Methods

.then() → runs when promise is fulfilled

.catch() → runs when promise is rejected

.finally()
→ runs always

myPromise.finally(() => {
console.log("Process finished");
});

Simple Summary**

Promise handles asynchronous operations

Makes code cleaner than callbacks

Used heavily with fetch, APIs, async/await