Floating-point cheat sheet for JavaScript

Floating-Point Types

JavaScript is dynamically typed and will often convert implicitly between strings and floating-point numbers (which are IEEE 64 bit values). To force a variable to floating-point, use the global parseFloat() function.

	var num = parseFloat("3.5");

Decimal Types

The oldest decimal type for JavaScript seems to be a port of Java’s BigDecimal class, which also supports rounding modes:

	var a = new BigDecimal("0.01");
	var b = new BigDecimal("0.02");
	var c = a.add(b); // 0.03
	var d = c.setScale(1, BigDecimal.prototype.ROUND_HALF_UP);

There is also bignumber.js, which is smaller and faster:

	BigNumber.config({ROUNDING_MODE: BigNumber.ROUND_HALF_UP})
	var a = new BigNumber("0.01");
	var b = new BigNumber("0.02");
	var c = a.plus(b); // BigNumber(0.03)
	var d = c.toFixed(1); // "0.0"

How to Round

	var num = 5.123456;
	num.toPrecision(1) //returns 5 as string
	num.toPrecision(2) //returns 5.1 as string
	num.toPrecision(4) //returns 5.123 as string

Using a specific rounding mode:

	new BigDecimal("1.25").setScale(1, BigDecimal.prototype.ROUND_HALF_UP);


© Published at floating-point-gui.de under the Creative Commons Attribution License (BY)

Fork me on GitHub