Beginner’s Guide #1: if (data) vs if (!!data) in JavaScript 🤔

#javascript #webdev #programming #beginners

Many beginners (and even some more advanced developers) run into this very common case in software development.

We want to execute some code only if a variable has a value.

There are two ways to write this check:

if (data) {
  // do something
}

and

if (!!data) {
  // do something
}

Both are correct ✅ and will give the same result.
The difference is style and intention.

✨ if (data)

This is the cleanest and most idiomatic way.
JavaScript automatically converts the value to true or false.
It’s simple, short and very readable.

🔍 if (!!data)

Here we force an explicit conversion to boolean.
Maybe a bit more descriptive, since it shows that we definitely want a true/false value.

👉 But inside an if statement this is redundant – because if already does that conversion for us.

⚡ Performance?

Let’s be honest. These two will always give the same result.
And even if there was some micro difference in performance, it’s negligible – you’ll never notice it, even inside loops.

So in practice, the shorter if (data) is the more elegant one. But is it only about syntax? 🤔

🧩 Falsy values explained

When I see someone using !! in an if, I sometimes wonder if they really understand type coercion and falsy values in JavaScript.

Falsy values are those that, in a logical context (if, &&, ||, !, Boolean()), always evaluate to false.

Here’s the full list (there are only 8 of them! 🎯):

false
0
-0 (negative zero)
0n (BigInt zero)
"" (empty string)
null
undefined
NaN

Everything else is truthy — it becomes true when converted to boolean.

⚖️ Examples

"0"         // truthy (string, not number 0)
"false"     // truthy (string, not boolean false)
[]          // truthy (empty array is still an object)
{}          // truthy (empty object too)
function() {}  // truthy