Why Does console.log() Sometimes Show Unexpected Values in JavaScript?

Sometimes we write console.log() and the output surprises us.

This usually happens because of:

Scope issues

Closures

Asynchronous behavior

But let’s understand this in a very simple way.

🔹 Simple Real-Life Example

Imagine you tell your friend:

“Tell me the number after 2 seconds.”

Now, before 2 seconds pass, you change the number.

When your friend finally speaks,
he tells the latest number, not the old one.

JavaScript works in a similar way.

Sometimes console.log() runs later,
and by that time the value has already changed.

🔹 Simple Code Example

for (var i = 1; i <= 3; i++) {
  setTimeout(() => {
    console.log(i);
  }, 1000);
}

You might expect:
1
2
3
But it prints:
3
3
3
Why?

Because:

var does not create block scope

The loop finishes first

i becomes 3

Then console.log() runs

So it prints the final value.

🔹 The Real Reason (In Simple Words)

console.log() sometimes shows unexpected values because:

The variable changed before the log executed

JavaScript waited before running the code

Scope was not handled properly

One-line Summary

Most unexpected console.log() results happen because of scope or async timing.