There are many great ways to improve your coding skills, experiment with new technologies. The truth of the matter is to understand JavaScript and Promise.

Part 1:

const prom = new Promise((res, rej) => {
  console.log('first');
  res();
  console.log('second');
});
prom.then(() => {
  console.log('third');
});
console.log('fourth');

// first
// second
// fourth
// third

Promise executes synchronously, promise.then executes asynchronously

Part 2:

const prom = new Promise((res, rej) => {
  setTimeout(() => {
    res('success');
  }, 1000);
});
const prom2 = prom.then(() => {
  throw new Error('error');
});

console.log('prom', prom);
console.log('prom2', prom2);

setTimeout(() => {
  console.log('prom', prom);
  console.log('prom2', prom2);
}, 2000);

// prom 
// Promise {<pending>}
// __proto__: Promise
// [[PromiseStatus]]: "resolved"
// [[PromiseValue]]: "success"

// prom2
// Promise {<pending>}__proto__: 
// Promise[[PromiseStatus]]: "rejected"[[PromiseValue]]: 
// Error: error
//     at <anonymous>:7:9

promise has three different states:

• pending
• fulfilled
• rejected

Once the status updated, pending->fulfilled or pending->rejected, it can be changed again. The prom1 is different from prom2 and both of them return new Promise status.

#javascript #promises in javascript