How to Check if a Variable Exists and is Initialized in JavaScript

General Discussions
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1

What’s the best way in JavaScript to check if a variable exists and is initialized, regardless of its type?

This version keeps the intent intact, flows conversationally, and smoothly includes the keyword javascript check if variable exists.

2

With about a decade dabbling in JavaScript, I can confidently say the most universal safeguard is:

if (typeof myVar !== 'undefined') {
  console.log("It exists!");
}

This typeof check is super safe because it doesn’t blow up even if myVar was never declared. It’s my default when building robust javascript check if variable exists logic — especially when I want to avoid those ugly reference errors that can halt execution. Whether you’re working across modules or loose scripts, this one’s reliable.

3

Totally agree with Charity! Building on that, in my experience with browser-based projects, there’s an extra trick when you’re specifically dealing with global variables:

if (window.hasOwnProperty('myVar')) {
  console.log("Global var exists!");
}

This dives a little deeper into javascript check if variable exists by confirming not just that myVar is defined, but that it’s part of the global window object. It’s niche, yes, but I’ve found it valuable when debugging things that should live in the global scope — especially when integrating legacy scripts or third-party libraries.

4

And here’s something I often layer on in more controlled setups: the good old truthy check.

if (myVar) {
  console.log("Yep, it's there and truthy!");
}

This style of javascript check if variable exists is super concise — but beware! It only works if myVar is already declared and holds a truthy value. So if it’s 0, false, null, or "", it’ll skip over. I usually reach for this in internal apps where the shape of the data is predictable and I just want to quickly verify meaningfulness without extra ceremony.