JavaScript Gotchas That Still Catch You Slipping (Even After Years)

[Sascha]

Yep — even an empty array is truthy. Try this:


if ([]) console.log("true"); // It runs!




Then your “harmless” condition silently fails elsewhere. Been there? These tiny quirks can break production logic in the weirdest ways.

The Scope Chain Dance


var count = 1;
if (true) {
var count = 2;
}
console.log(count); // 2




Now switch to let or const and the behavior changes.

Lesson: If you're still casually using var in 2025 — you're skating on thin ice.

OOP vs Functional

Someone asked me: “Which is better — OOP or Functional?

My answer: Depends.

OOP helps when you're modeling real-world structures (ex: User, Order, Cart)
Functional shines when transforming data pipelines (ex: map(), filter(), reduce())

Real Use: I mixed both in a React-Redux app — OOP-style classes for config, FP-style for transformation — and it worked beautifully.

The DOM: Knowing It vs Using It

Many devs use JS or React to manipulate the DOM — but few understand how it really works under the hood.


document.body.children[0].textContent;




Looks old-school? It once helped me debug a script before React mounted.

Why it matters: DOM knowledge is critical when:

1. Tuning performance
2. Fixing bugs in third-party scripts
3. Understanding how React actually mounts

JSON.stringify() vs JSON.parse()


const data = JSON.stringify({ price: 100 });
const parsed = JSON.parse(data);




Clean, right? Now try:

JSON.parse(undefined);
Real APIs don’t always come wrapped with love and structure.

Lesson: Always validate before parsing.

Use try...catch:


try {
const safeParsed = JSON.parse(data);
} catch (error) {
console.error("Parsing failed:", error);
}




Final Thought

JavaScript doesn’t just run — it behaves. Sometimes… unexpectedly. And knowing those behaviors is what separates a dev from a debugger.

What’s your most “Wait… what just happened?” JS moment?

Drop your logic bugs, type coercion fails, or memory leaks below , Let’s laugh, cry, and learn together.

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