Math.sumPrecise()

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The Math.sumPrecise() static method takes an iterable of numbers and returns the sum of them. It is more precise than summing them up in a loop, because it avoids floating point precision loss in intermediate results.

Try it

console.log(Math.sumPrecise([1, 2]));
// Expected output: 3

console.log(Math.sumPrecise([1e20, 0.1, -1e20]));
// Expected output: 0.1

Syntax

Math.sumPrecise(numbers)

Parameters

numbers: An iterable (such as an Array) of numbers.

Return value

A number that is the sum of the numbers in the numbers iterable. If the iterable is empty, the return value is -0 (not 0).

Exceptions

TypeError: If numbers is not an iterable, or if any of the numbers in the iterable is not of the number type.

Description

Because sumPrecise() is a static method of Math, you always use it as Math.sumPrecise(), rather than as a method of a Math object you created (Math is not a constructor).

The method is called Math.sumPrecise() because it is more precise than naïvely summing up numbers in a loop. Consider the following example:

let sum = 0;
const numbers = [1e20, 0.1, -1e20];
for (const number of numbers) {
  sum += number;
}
console.log(sum); // 0

The output is 0. This is because 1e20 + 0.1 cannot be represented precisely in 64-bit floats, so the intermediate result is rounded to 1e20. Then, the sum of 1e20 and -1e20 is 0, so the final result is 0.

Math.sumPrecise() avoids this issue by using some specialized summing algorithm. It works as if the floating point numbers are summed up using their precise mathematical values, and the final result is then converted to the nearest representable 64-bit float. This still cannot avoid the 0.1 + 0.2 precision problem:

console.log(Math.sumPrecise([0.1, 0.2])); // 0.30000000000000004

Because the floating point literals 0.1 and 0.2 already represent mathematical values greater than 0.1 and 0.2, and their sum's closest 64-bit float representation is actually 0.30000000000000004.

Examples

Using Math.sumPrecise()

console.log(Math.sumPrecise([1, 2, 3])); // 6
console.log(Math.sumPrecise([1e20, 0.1, -1e20])); // 0.1

Specifications

Specification
Math.sumPrecise # sec-math.sumprecise

Browser compatibility

	Desktop					Mobile						Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	Deno	Node.js
`sumPrecise`	No	No	137	No	preview	No	137	No	No	No	No	No	No