Promise

A Promise in JavaScript is an object representing the eventual completion or failure of an asynchronous operation, typically a network request, file I/O operation, or a database query.

A Promise has three states:

Pending: The initial state, before the Promise is resolved or rejected.
Resolved/Fulfilled: The operation completed successfully and the Promise has a resulting value.
Rejected: The operation failed and the Promise has a reason for the failure.

A Promise has two parts:

The producer: The code that initiates the asynchronous operation, which returns a Promise object.
The consumer: The code that uses the Promise object to get the result or handle the error.

A Promise is created using the Promise constructor, which takes a function that receives two arguments: a resolve function and a reject function. The resolve function is called when the operation completes successfully and the reject function is called when the operation fails. The Promise object returned by the constructor is then used by the consumer to get the result or handle the error.

Here is an example of creating and using a Promise in JavaScript:

const promise = new Promise((resolve, reject) => {
  // Perform an asynchronous operation, such as a network request or file I/O
  const result = ...; // the result of the operation
  if (result) {
    // Resolve the Promise with the result
    resolve(result);
  } else {
    // Reject the Promise with an error
    reject(new Error('Something went wrong'));
  }
});

// Use the Promise to get the result or handle the error
promise.then((result) => {
  // Handle the successful result
}).catch((error) => {
  // Handle the error
});

Promise

META