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How to setTimeout Synchronously in JavaScript

· One min read
Santanu Panda
Santanu Panda
Cloud Engineer @ Cisco

Overview​

In JavaScript, setTimeout is an asynchronous function, meaning it does not block the execution of subsequent code. However, you can achieve a synchronous-like delay using Promises and the async/await pattern.

Implementation​

You can create a sleep function that returns a Promise, which resolves after the specified timeout:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

Then, use await inside an async function to pause execution until the Promise resolves:

async function demo() {
  await sleep(5000);
  alert('This should be the second one');
}

demo();

Explanation​

  1. The sleep function returns a Promise that resolves after ms milliseconds.
  2. Inside the demo function, await sleep(5000); pauses execution for 5 seconds.
  3. After the delay, the alert message is displayed.

Using await ensures that the execution flow appears synchronous, making the code more readable and manageable in asynchronous scenarios.