Why does `0.1 + 0.2 === 0.3` return false in JavaScript?

Question

I was writing a small invoice calculator and this check fails:

```js
console.log(0.1 + 0.2 === 0.3); // false
console.log(0.1 + 0.2);         // 0.30000000000000004
```

Is this a bug in JavaScript? How should I compare or add money amounts?

Accepted Answer

It's not a JavaScript bug. It's how IEEE-754 binary floating point works, and Python, Java and C# do exactly the same thing. `0.1` has no exact binary representation, so tiny rounding errors show up.

**Comparing floats:** use a tolerance.

```js
const nearlyEqual = (a, b) => Math.abs(a - b) < Number.EPSILON * 10;
nearlyEqual(0.1 + 0.2, 0.3); // true
```

**Money:** never store it as floating point. Store **integer cents** (or the smallest unit, e.g. centimes of a gourde):

```js
const totalCents = 1050 + 299; // 13.49
const display = (totalCents / 100).toFixed(2);
```

For heavy financial math, use a decimal library such as `decimal.js`, or do it in the database with a `NUMERIC` column.

2 Repons