Introduction to Promises

Promises

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

Example

const p = new Promise((resolve, reject) => {
  setTimeout(() => resolve("done!"), 1000);
});
p.then(val => console.log(val))   // "done!"
 .catch(err => console.error(err))
 .finally(() => console.log("always runs"));

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Pro Tip

Always attach a .catch() — unhandled rejections crash Node and log warnings in browsers.

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