Why a small rounding error matters

Try this in your browser console or Node.js:

console . log ( 0.1 + 0.2 ); // 0.30000000000000004

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This is expected behavior, not a JavaScript bug. The Number type uses IEEE 754 binary floating-point values, so many decimal fractions cannot be represented exactly.

That usually isn't a problem when you're positioning an element on a page. It becomes a problem when a value represents a cryptocurrency balance, transfer amount, fee, or transaction limit.

For financial amounts, the goal is not to hide floating-point artifacts with formatting. It's to avoid introducing them into the calculation.

Let's build a small JavaScript utility that parses decimal amounts into integer base units, performs exact arithmetic, and formats the results without converting back to Number .

The code below is a standalone educational example, not a description of any particular exchange's production implementation.…