The Bug Wasn't in My Code --- It Was in My Assumptions 🤯

We've all been there.

The code looks correct.

No obvious syntax errors.
The logic seems fine.
You read the same function 10 times.

And somehow...

It still doesn't work. 😭

After wasting way too much time debugging situations like this, I
realized something:

Sometimes the bug isn't in your code. It's in what you assumed about
your code.

The classic debugging trap

Imagine you're calling an API and expecting this:

{
  "user": {
    "name": "Ash"
  }
}

So naturally, you write:

const name = response.user.name;

Everything looks perfectly reasonable.

But the actual response is:

{
  "data": {
    "user": {
      "name": "Ash"
    }
  }
}

Now you're staring at your JavaScript wondering:

"Why is user undefined?!"

The JavaScript isn't necessarily the problem.

Your assumption about the API response was.

This happens everywhere

It's not just API responses.

You can make incorrect assumptions about:

• What data a function receives
• Whether a value can be null
• What an API actually returns
• Environment variables being available
• File paths
• Database records
• Authentication state
• Time zones
• User input
• Production vs development environments
• What a third-party library actually does

And these assumptions can create some seriously confusing bugs.

My new debugging approach

Instead of immediately changing the code, I try to verify my assumptions
first.

1. What do I think is happening?

Write down your assumption.

For example:

"The API is returning the user object."

2. What is actually happening?

Inspect the data.

console.log(response);

Don't guess.

Look at it.

3. Where does reality differ from my assumption?

Maybe the API response changed.

Maybe the value is undefined.

Maybe the environment variable isn't loaded.

Maybe the backend is returning an error that the frontend isn't
handling.

4. Fix the actual problem

Only after understanding the mismatch should you change the code.

This saves a surprising amount of time.

The debugging rule I now follow

When something doesn't make sense, I ask:

"What am I assuming right now that I haven't verified?"

That question is surprisingly powerful.

Because debugging isn't always about finding the broken line.

Sometimes it's about finding the wrong mental model.

A simple debugging checklist

Next time you're stuck, check:

☐ What input am I actually receiving?
☐ What output am I actually getting?
☐ Did I verify the API response?
☐ Could this value be undefined/null?
☐ Are my environment variables loaded?
☐ Am I testing the same environment as production?
☐ Did the data structure change?
☐ Am I assuming something instead of checking it?

Final takeaway

Good debugging isn't just:

"Find the broken code."

It's:

"Find the difference between what I expected and what is actually
happening."

Once you start debugging your assumptions, some of those
"impossible" bugs become surprisingly easy to solve.

And honestly...

Sometimes the most useful debugging tool isn't another console.log.

It's asking:

"Wait... how do I know that's actually true?" 👀

---

What about you?

What's a bug that took you way too long to fix because you were making
the wrong assumption?

Drop it in the comments 👇