Math.max() returns the largest of zero or more numbers passed to it. We can use the spread operator when passing an array to get the largest number from that array.
// get the largest number from a list of numbers
Math.max(69, 420, 108, 47) // ⇒ 420
// passing an array instead of individual numbers returns `NaN`
const numbers = [69, 420, 108, 47]
Math.max(numbers) // ⇒ NaN
// we get the expected result by spreading the array
const numbers = [69, 420, 108, 47]
Math.max(...numbers) // ⇒ 420
Top comments (13)
In any sane programming language, you'd just do
but alas, JS masterfully breaks every existing pattern except those coming from C.
I think you're picking a hole in JS where there isn't one, except, perhaps, in the
Math.maxfunction. You could easily create a function which will work very happily with reduce:Nice alternative! That is the way I used to do this before the spread operator. Works just as well.
You might want to safeguard this with Number.NEGATIVE_INFINITY as the initial value in
reducein case of an empty array.Math.max()also returns-Infinitywhen called without any parameters.That'd surely be worth doing, I really only added that code to give an example close to the code that was quoted.
Fair enough. 👍
There definitely is. The problem here is a clash between two good intentions:
The first one is unnecessary. It's only a bit more convenient to write
max(a, b, c)than[a, b, c].fold(max), but it's still something that makes sense.The second one, on the other hand, is a giant footgun. It only makes sense in the context of optimization, as using
mapfirst would result in one temporary array being created, but that should be optimized by the language runtime via stream fusion, not by the specification of the function. Ultimately it will just lead to more confusing code full of functions that do too many things at once, giving it a very procedural feel.As for your solution, that's basically what I did, except that I wrote the function inline. Another solution would be:
Which, to prevent monkey-patching, sadly loses the method-syntax which makes chaining easier to read.
I'm sure there are many situations where it's preferable to pass multiple arguments instead of constructing a whole new array to do max. I may find it preferable today to construct an array and use array methods to manipulate it, but those methods are, relatively speaking, very new additions to the language.
Regarding:
I've not yet used a language which doesn't allow providing a seed value into its reduction function. Haskell's foldr requires it. Cloure's reduce allows it. C#'s
Aggregateallows it to be specified. I wouldn't want to work with a language that didn't allow me to specify a seed value this way.I appreciate that I wrote basically the same code example that you did - I was trying to point out that there's not any issue at all with reduce in js, it just isn't called fold.
The seed value is not the problem here. The combining function should take two arguments, but
reducepasses 4, which is both dumb and the cause of this problem. I haven't seen another language that does this.Well, there is: it passes two extra arguments to the combining function, which no other fold function usually does.
Ah I see your point now, sorry I misunderstood what you were saying originally, my bad.
It is frustrating, but really we're talking about edge cases here where you're looking to pass variadic functions into
Array.reduce. In this instance we're hitting a problem due to the fact that, firstly,Math.maxis variadic and secondly thatArray.reducepasses additional arguments by default. Agreed that neither of those is ideal.JS really isn't a language of ideals, though - it's a pragmatic scripting language, and, for all its flaws, it allows people to get things done quickly. For me a big part of being a good JS programmer is learning to live with its flaws, because if you obsess over them, you can't get very far with it.
I agree you could do the same with
reduceif you’d prefer that. I prefer the shorter version, but that’s why it’s good there are many ways to do the same thing. I wouldn’t call JavaScript “insane” because it does some things differently.In your example, you probably want to use Number.NEGATIVE_INFINITY instead of
0as the initial value in case there are only negative values in the array.You can just pass it a single argument. I tried that at first but changed it because I thought that was causing my error, but then I figured out it was actually
reducepassing additional garbage toMath.max.It's not that it does things differently that makes insane. It's the fact that it does things differently in insane ways. Passing random stuff nobody wanted to the combining function in
reduceis one such thing, but there's many many more.If you don't have to deal with large arrays (more than 100000 elements), then this approach works fine.
However if the array is large, please bear in mind that JavaScript runtimes have a limitation on the number of arguments that you can pass to a function. Yes, this include spread parameters.
If you pass more arguments than the limit, “Maximum call stack size exceeded” errors happen.
I have to find the maximum and minimum value of very huge arrays. For this I'm using
It works good on Firefox and IE, but on Chrome I always get
Maximum call stack size exceedederrors... my current array has 221954 elements, and that's not my…It looks like this works, too.