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.