How to Check JavaScript Version in Your Browser or Environment

JavaScript does not have a direct version number you can check with code because browsers implement ECMAScript standards incrementally. Instead, use feature detection to test if specific JavaScript features are supported or check your browser's developer console for the JavaScript engine version.

Syntax

There is no direct syntax to get a JavaScript version number because JavaScript evolves through ECMAScript standards. Instead, you check for features like this:

• if ('feature' in object) { ... } checks if a feature exists.
• Use console.log(navigator.userAgent) to see browser info.

javascript

if ('Promise' in window) {
  console.log('Promises are supported');
} else {
  console.log('Promises are NOT supported');
}

Output

Promises are supported

Example

This example shows how to detect if your environment supports modern JavaScript features like let, const, and arrow functions, which indicate newer JavaScript versions.

javascript

try {
  eval('let x = () => 5; const y = x();');
  console.log('Modern JavaScript features are supported');
} catch (e) {
  console.log('Modern JavaScript features are NOT supported');
}

Output

Modern JavaScript features are supported

Common Pitfalls

Many developers expect to get a JavaScript version number like software versions, but JavaScript is standardized by ECMAScript editions, and browsers implement features gradually. Relying on navigator.appVersion or navigator.userAgent strings to guess JavaScript version is unreliable.

Instead, always use feature detection to check if a feature you want to use is available.

javascript

/* Wrong way: Trying to get version from userAgent */
console.log(navigator.userAgent);

/* Right way: Feature detection example */
if ('fetch' in window) {
  console.log('Fetch API supported');
} else {
  console.log('Fetch API NOT supported');
}

Output

Fetch API supported

Quick Reference

Summary tips to check JavaScript support:

• Use feature detection for specific JavaScript features.
• Check browser developer console for JavaScript engine info.
• Do not rely on version numbers; JavaScript evolves by features.

Key Takeaways

JavaScript does not have a direct version number; it evolves by ECMAScript standards.

Use feature detection to check if a JavaScript feature is supported in your environment.

Avoid relying on browser version strings to guess JavaScript version.

Modern JavaScript features like arrow functions and promises indicate newer support.

Check your browser's developer console for JavaScript engine details if needed.