Promise in Javascript

JavaScript Promises make handling asynchronous operations like API calls, file loading, or time delays easier. Think of a Promise as a placeholder for a value that will be available in the future. It can be in one of three states

Pending: **The task is in the initial state.
**Fulfilled: The task was completed successfully, and the result is available.
**Rejected: **The task failed, and an error is provided.
Here is an example Promise to check if a number is even. If yes, it resolves; otherwise, it rejects.

Example

let checkEven = new Promise((resolve, reject) => {
    let number = 4;
    if (number % 2 === 0) resolve("The number is even!");
    else reject("The number is odd!");
});
checkEven
    .then((message) => console.log(message)) // On success
    .catch((error) => console.error(error)); // On failure

Note: The "resolve" and "reject" are not keywords. You can use any name that you want to give to a function.

Syntax

let promise = new Promise((resolve, reject) => {
// Perform async operation
if (operationSuccessful) {
resolve("Task successful");
} else {
reject("Task failed");
}
});

resolve(value): Marks the promise as fulfilled and provides a result.
reject(error): Marks the promise as rejected with an error.