numbers

Aniterable (such as anArray) of numbers.

A number that is the sum of the numbers in thenumbers iterable. If the iterable is empty, the return value is-0 (not0).

TypeError

Ifnumbers is not an iterable, or if any of the numbers in the iterable is not of the number type.

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

The method is calledMath.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 because1e20 + 0.1 cannot be represented precisely in 64-bit floats, so the intermediate result is rounded to1e20. Then, the sum of1e20 and-1e20 is0, so the final result is0.

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 the0.1 + 0.2 precision problem:

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

Because the floating point literals0.1 and0.2 already represent mathematical values greater than0.1 and0.2, and their sum's closest 64-bit float representation is actually0.30000000000000004.

• Polyfill ofMath.sumPrecise incore-js
• es-shims polyfill ofMath.sumPrecise
• Array.prototype.reduce()