Why is math.max() returning NaN on an array of integers?

Question

I am trying to get the highest number from a simple array:

data = [4, 2, 6, 1, 3, 7, 5, 3];

alert(Math.max(data));

I have read that if even one of the values in the array can't be converted to number, it will return NaN, but in my case, I have double-checked with typeof to make sure they are all numbers, so what can be my problem?

Softball

just see doc, about Math.max :-) If at least one of arguments cannot be converted to a number, the result is NaN. – Kunstlied

That's not a valid dupe in my opinion. This question is not how to do it, but more why does it not work with an array. The dupe question does not seem to answer this – Downes

@musefan, see link to doc above: this array just cannot be converted to a number :-) – Kunstlied

Oh, I didn't see the difference between passing an array of numbers to Math.max() instead of a comma-separated list of numbers... so in my original code, I was trying to get the max of [array] and [nothing else]. – Softball

@Grundy: Yeah I know the reason, I was just about to answer myself explaining the problem before it was closed. But my point stands, that dupe is not the same question, nor does it answer this question. It provides a solution sure, but it doesn't answer why it doesn't work with array of numbers – Downes

@MattWelander, so see answer in dup question – Kunstlied

@Downes You cannot call max on array, so as you can see in the answers of the #1669690 question, you're passing the Math as context and calling max function from Math and passing the array elements as individual parameters to max() – Minh

@musefan, but answer why it doesn't work with array of numbers stay in docs – Kunstlied

@Grundy: Yeah, so the answer to this question might be to reference that particular part of the docs. We don't close question because there is a document somewhere on the internet that answers it already – Downes

@musefan, so possibly you right :-) add vote to reopen – Kunstlied

@Tushar: Stop talking to me, you're obviously not cut out for this conversation. You appear to be under the impression I don't know the reason, and completely missing my point that the question is not a dupe. Show me an answer in that dupe that says why it doesn't work with arrays – Downes

@Downes in one answer from dupe link aaroncrane.co.uk/2008/11/javascript_max_api so, it a bit explain why :-) – Kunstlied

@Grundy: But links don't count. They are for supporting answers, not providing them. That link could break at anytime, especially as it looks like its a personal site – Downes

Answer 1

The reason why your code doesn't work is because Math.max is expecting each parameter to be a valid number. This is indicated in the documentation as follows:

If at least one of arguments cannot be converted to a number, the result is NaN.

In your instance you are only providing 1 argument, and that 1 value is an array not a number (it doesn't go as far as checking what is in an array, it just stops at knowing it isn't a valid number).

One possible solution is to explicitly call the function by passing an array of arguments. Like so:

Math.max.apply(Math, data);

What this effectively does is the same as if you manually specified each argument without an array:

Math.max(4, 2, 6, 1, 3, 7, 5, 3);

And as you can see, each argument is now a valid number, so it will work as expected.

Spreading an array

You can also spread the array. This essentially treats the array as if each item is being passed as it's own argument.

Math.max(...data);

Downes

Answer 2

if you see doc for Math.max you can see next description

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

If no arguments are given, the result is -Infinity.

If at least one of arguments cannot be converted to a number, the result is NaN.

When you call Math.max with array parameter like

Math.max([1,2,3])

you call this function with one parameter - [1,2,3] and javascript try convert it to number and get ("1,2,3" -> NaN) fail.
So result as expected - NaN

NOTE: if array with just one number - all work correctly

 Math.max([23]) // return 23

because [23] -> "23" -> 23 and covert to Number is done.

---

If you want get max element from array you should use apply function, like

Math.max.apply(Math,[1,2,3])

or you can use the new spread operator

Math.max(...[1,2,3])

Kunstlied

Answer 3

It's not working because you are passing an array as the parameter instead of comma separated numbers. Try spreading the array like this:

data = [4, 2, 6, 1, 3, 7, 5, 3];    
alert(Math.max(...data));

Millihenry

Answer 4

If you have to use the Math.max function and one number of the array might be undefined, you could use:

x = Math.max(undefined || 0, 5)
console.log(x) // prints 5

Reginiaregiomontanus

Answer 5

You will need to use the spread operator while passing array as an argument to the Math.max() method.

alert(Math.max(...data)); //this should resolve it.

Peeples