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JavaScript has only one number type: a 64-bit IEEE 754 floating-point. No separate int and float types like most languages. That keeps the language simple, but it has consequences you should know.

The arithmetic operators

There's no separate integer-divide operator. Use Math.floor(a / b) for that:

Math.floor rounds toward negative infinity. Math.trunc chops the decimal. They differ for negatives.

The float-precision surprise

Because all numbers are IEEE 754 floats, you'll hit a famous quirk:

Don't compare floats with === directly. For "close enough":

For money: never use plain numbers. Either work in cents (integers) or use a decimal library.

Special numeric values

NaN propagates: any arithmetic involving NaN produces NaN. To detect it, use Number.isNaN(x), NOT x === NaN.

BigInt — for arbitrary-precision integers

For integers larger than Number.MAX_SAFE_INTEGER (2⁵³−1), use BigInt:

BigInt and Number can't be mixed in arithmetic — convert with BigInt(x) or Number(b).

Parsing strings to numbers

Always pass the radix to parseInt (parseInt(s, 10) for decimal). Without it, strings starting with 0 were historically interpreted as octal.

Useful Math methods

For a random integer in [0, n): Math.floor(Math.random() * n).

Common mistakes

• Comparing floats with ===. Use Math.abs(a - b) < Number.EPSILON.
• Using x === NaN. Always returns false. Use Number.isNaN(x).
• Forgetting the radix in parseInt.
• Using plain numbers for money. Work in cents or use Decimal.js.