Numbers and the Math Object

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Numbers

JavaScript has a single number type that represents both integers and floating-point numbers as 64-bit IEEE 754 doubles. This means integers up to 2^53 − 1 are exact; beyond that, use BigInt.

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console.log(0.1 + 0.2);         // 0.30000000000000004
console.log(Number.isFinite(1/0)); // false (Infinity)
console.log(Number.isNaN(0/0));    // true
console.log(Number.isInteger(3.0)); // true

// Parsing
Number.parseInt("42px");     // 42
Number.parseFloat("3.14em"); // 3.14
Number("42");                // 42
Number("");                  // 0
Number("abc");               // NaN

The Math Object

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Math.round(4.6);   // 5
Math.floor(4.9);   // 4
Math.ceil(4.1);    // 5
Math.abs(-7);      // 7
Math.max(1, 5, 3); // 5
Math.min(1, 5, 3); // 1
Math.pow(2, 10);   // 1024
Math.sqrt(144);    // 12
Math.trunc(-4.7);  // -4
Math.random();     // [0, 1)

// Random integer in [min, max]
const rand = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

For financial calculations, avoid floating-point arithmetic altogether. Work in the smallest currency unit (cents) as integers, or use a decimal library. 0.1 + 0.2 !== 0.3 is a real bug in money code.

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