Node.js Timers Module

What is the Timers Module?

Key features include:

Delayed execution with setTimeout()

Repeated execution with setInterval()

Promise-based APIs for modern async/await patterns

Getting Started with Timers

Basic Timer Example

const { setTimeout, setInterval, setImmediate } = require('timers');
console.log('Starting timers...');
// Execute once after delay setTimeout(() => {
console.log('This runs after 1 second');
}, 1000);
// Execute repeatedly at interval let counter = 0;
const interval = setInterval(() => {
counter++;
console.log(`Interval tick ${counter}`);
if (counter >= 3) clearInterval(interval);
}, 1000);
// Execute in the next event loop iteration setImmediate(() => {
console.log('This runs in the next iteration of the event loop');
});
console.log('Timers scheduled');

Using the Timers Module

const timers = require('timers');
// Or, for the promises API (Node.js 15.0.0+)
const timersPromises = require('timers/promises');
setTimeout() and clearTimeout()
The setTimeout() function schedules execution of a callback after a specified amount of time (in milliseconds).

It returns a

Common Use Cases

Delaying execution of non-critical tasks

Implementing timeouts for operations

Breaking up CPU-intensive tasks

Implementing retry logic

// Basic usage setTimeout(() => {
console.log('This message is displayed after 2 seconds');
}, 2000);
// With arguments setTimeout((name) => {
console.log(`Hello, ${name}!`);
}, 1000, 'World');
// Storing and clearing a timeout const timeoutId = setTimeout(() => {
console.log('This will never be displayed');
}, 5000);
// Cancel the timeout before it executes clearTimeout(timeoutId);
console.log('Timeout has been cancelled');

Promise-Based setTimeout

Node.js 15.0.0 and later provide a promises - based API for timers:

const { setTimeout } = require('timers/promises');
async function delayedGreeting() {
console.log('Starting...');
// Wait for 2 seconds await setTimeout(2000);
console.log('After 2 seconds');
// Wait for 1 second with a value const result = await setTimeout(1000, 'Hello, World!');
console.log('After 1 more second:', result);
}
delayedGreeting().catch(console.error);
setInterval() and clearInterval()
The setInterval() function calls a function repeatedly at specified intervals (in milliseconds).

It returns an

Common Use Cases

Polling for updates

Running periodic maintenance tasks

Implementing heartbeat mechanisms

Updating UI elements at regular intervals

Note:

// Basic interval let counter = 0;
const intervalId = setInterval(() => {
counter++;
console.log(`Interval executed ${counter} times`);
// Stop after 5 executions if (counter >= 5) {
clearInterval(intervalId);
console.log('Interval stopped');
}
}, 1000);
// Interval with arguments const nameInterval = setInterval((name) => {
console.log(`Hello, ${name}!`);
}, 2000, 'Node.js');
// Stop the name interval after 6 seconds setTimeout(() => {
clearInterval(nameInterval);
console.log('Name interval stopped');
}, 6000);

Promise-Based setInterval

const { setInterval } = require('timers/promises');
async function repeatedGreeting() {
console.log('Starting interval...');
// Create an async iterator from setInterval const interval = setInterval(1000, 'tick');
// Limit to 5 iterations let counter = 0;
for await (const tick of interval) {
console.log(counter + 1, tick);
counter++;
if (counter >= 5) {
break; // Exit the loop, stopping the interval
}
}
console.log('Interval finished');
}
repeatedGreeting().catch(console.error);
setImmediate() and clearImmediate()
The setImmediate() function schedules a callback to run in the next iteration of the event loop, after I/O events but before timers.
It's similar to using setTimeout(callback, 0)

When to Use setImmediate()

To break up long - running operations into smaller chunks
To ensure callbacks run after I/O operations complete

In recursive functions to prevent stack overflows console.log('Start');
setTimeout(() => {
console.log('setTimeout callback');
}, 0);
setImmediate(() => {
console.log('setImmediate callback');
});
process.nextTick(() => {
console.log('nextTick callback');
});
console.log('End');