What is a Promise?

Promises are a language feature that allows developers to write asynchronous code in a synchronous style. They provide a way to handle asynchronous operations in a way that is easier to read.

function delayedFn(ms) {
    return new Promise((resolve, reject) => {
        console.log('Running a promise with status: pending')
    
        if (ms < 1000) {
            reject('Too little time - It must be more than 1000 ms!');
        } else {
            setTimeout(() => resolve(ms), ms);
        }
    });
}

delayedFn(900)
    .then((ms) => console.log(`Promise with status: fulfilled; after: ${ms} ms!`))
    .catch(err => console.error('Promise with status: rejected and error', err))
    .finally(() => console.log('Always works!'))