Q496: How does JavaScript handle floating point precision issues? - JavaScript Internals (521 Qs)

JavaScript uses IEEE 754 double-precision (64-bit) floating-point format, which can cause precision issues with decimal numbers.

javascript

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

Solutions:

Using epsilon comparison:

javascript

    function areEqual(a, b) {
      return Math.abs(a - b) < Number.EPSILON;
    }
    console.log(areEqual(0.1 + 0.2, 0.3)); // true

Rounding to fixed decimals:

javascript

    const result = Math.round((0.1 + 0.2) * 100) / 100; // 0.3

Using toFixed() or toPrecision():

javascript

    const sum = (0.1 + 0.2).toFixed(2); // "0.30"
    const num = parseFloat(sum); // 0.3

Working with integers (cents instead of dollars):

javascript

    const price1 = 10; // $0.10 as 10 cents
    const price2 = 20; // $0.20 as 20 cents
    const total = price1 + price2; // 30 cents
    const dollars = total / 100; // $0.30

Using libraries for precise calculations:

javascript

    // decimal.js, big.js, or bignumber.js
    const Decimal = require('decimal.js');
    const result = new Decimal(0.1).plus(0.2); // 0.3