Promises Deep Dive (Chaining, States, Errors)

What Is a Promise?

A Promise represents a value that will be available in the future. It can be in one of three states: pending, fulfilled, or rejected.

Creating a Promise

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('done');
  }, 1000);
});

Consuming a Promise

promise
  .then(result => console.log(result))
  .catch(error => console.error(error));

Chaining

Promises allow chaining, which prevents callback nesting.

Error Handling

Errors thrown inside a promise automatically propagate to the nearest catch handler.

Production Insight

Always return promises in chains. Missing returns cause silent async bugs.