Why should you care?

Browsers cannot freeze while waiting for a network response. Promises let other code keep running.

See it live — copy this example

Paste into an HTML file or the browser console (F12). Use Run below when the live editor is available.

function wait(ms) {
  return new Promise((resolve) => {
    setTimeout(() => resolve("Done after " + ms + "ms"), ms);
  });
}

wait(500).then((msg) => console.log(msg));

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What happened?

• new Promise takes a function with resolve.
• setTimeout runs after 500ms, then resolve sends the message to .then().

Practice next

1. Run wait(500).then and observe delay.
2. Chain two waits in sequence.
3. Add .catch on a rejecting promise.
4. Return Promise.all on two wait calls to run in parallel.
5. Reject intentionally and log in catch with a custom message.

Remember

Promise = future value .then for success, .catch for errors Used by fetch and timers

ScriptVerse parallel fetch

Dashboard loads accounts and notifications with Promise.all before hiding the skeleton loader.

Outcome: Promises coordinate multiple API calls without callback nesting.