A proposal to add a method to sum multiple values to JavaScript.
Authors: Kevin Gibbons
Champions: Kevin Gibbons
This proposal is at Stage 1 of the TC39 process: the proposal is under consideration.
Summing a list is a very common operation and is one of the few remaining use cases for Array.prototype.reduce. Better to let users express that operation directy.
Also, summing a list of floating point numbers can be done more precisely than the naive .reduce((a, b) => a + b, 0) approach using more clever algorithms, a fact which few JavaScript programmers are aware of (and even among those who are, most wouldn't bother doing it). We can make it easy to reach for the better option.
Add a variadic Math.sum method which returns the sum of its arguments using a more precise algorithm than naive summation.
let values = [1e20, 0.1, -1e20];
values.reduce((a, b) => a + b, 0); // 0
Math.sum(...values); // 0.1Instead of specifying any particular algorithm, this proposal requires the maximally correct answer - that is, the answer you'd get if you did arbitrary-precision arithmetic, then converted the result back to floats. This can be done without actually needing arbitrary-precision arithmetic. One way of doing this is given in Shewchuk '96, which I've implemented in JS (plus some details to handle intermediate overflow). Other strategies are possible.
Python's math.fsum is currently implemented using the same algorithm (though without handling intermediate overflow).
I'd like to have a version which works with iterables. Unfortunately Math.max sets precedent that such methods are variadic, so Math.sum probably will need to be as well.
In my ideal world we would also add Math.maxFrom and Math.sumFrom (or some other, better names) which operate on iterables instead of varargs.
I want to stop coercing things, but unfortunately Math.max is pretty strong precedent that we do coercion.
I'm hopeful that engines will be able to have a fast path when they know everything is a Number already, at least for the iterable-taking version.
No - it's important that Math.sum() returns the Number -0, which means that 5n + Math.sum(...bigints) would throw when bigints is empty, which would be bad.
We should have seperate methods for summing BigInts. I'd vote for BigInt.sum. Maybe as part of this proposal, maybe not.
That comes up much less so I'm not currently proposing it.
Math.max uses 2, so that's what I'm defaulting to, but it doesn't really matter and if you feel strongly it should be some other thing feel free to send a PR making the change and a case for it.