What-is-the-value-of-Math.max_2_3_4_5_.md

Question: What is the value of Math.max([2,3,4,5]);

Answer: NaN

Explanations

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.

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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])

Alternative way to achieve the same above

The above Math.max([2,3,4,5]); was producing NaN - because I was 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));

Further Alternative and more explanations

The reason why this is happening is that Math.max calculates the maximum out of its parameters. And seen as the first parameter is an Array it returns NaN.

You now have 2 options (depending on your environment or preference):

ES6 (with spread syntax)

You can spread the array to the params of the function.

const thenum = [5, 3, 678, 213];

console.log(Math.max(...thenum));

More on the spread syntax

And here is a jsFiddle with this example.

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ES5 (without spread syntax)

Or, you can call it using the apply method which allows you to call functions and send the parameters for them within an array.

What you want is to apply the Math.max function, like so:

var thenum = [5, 3, 678, 213];

function max(num){
    return Math.max.apply(null, num);
}

console.log(max(thenum));

You can also make it a method and attach it to the Array prototype. This way you can use it easier and cleaner (overwriting the prototype is dangerous and you should probably avoid it - Read more about it). Like so:

Array.prototype.max = function () {
    return Math.max.apply(null, this);
};
console.log([5, 3, 678, 213].max());

More on the apply method.

And here is a jsFiddle with both