As per Sebastian’s comment: your requestCount is almost certainly a string instead of a number:
new Array(4).fill()
// Array(4) [ undefined, undefined, undefined, undefined ]
new Array("4").fill()
// Array(1) [ undefined ]
In fact the second constructor does something wildly different from the first one. new Array(int) will create an Array with <int> empty slots. However, new Array(not-an-int) will create an array with the constructor arguments as content, so:
new Array(4)
// Array(4) [ <4 empty slots> ]
new Array("4")
// Array(1) ["4"]
So if we call .fill() without any argument, we’re saying “replace the content for all elements with undefined“, and we have an array containing a single element (the string “4”), then we end up with [undefined].
The lesson here is to always validate your inputs before you pass them to functions/constructors that are polymorphic with respect to argument type:
const requestCount = await campaign.methods.getRequestsCount().call();
// I don't know what that line can return, so verify that there even
// _is_ a result. If there is, then we can continue:
const n = parseInt(requestCount);
if (isNaN(n)) {
// this is a probably something you should have a contingency for
}
// and if n _is_ a number, it also needs to make sense as an array length value
else if (n > 0) {
const mapped = [...Array(n)].map((_,i) => {
// do something with i
});
}
But that “convenient syntax” using map basically wastes time on creating an array that we’re then immediately throwing away. That’s silly: we can achieve the exact same result without immediately invoking garbage collection by using array’s stack functions:
// note: let, not const, because we're going to run it down to 0
let n = .....
...code that returns early based on bad values of n...
const mapped = [];
while(n--) {
// since we're running our index backwards, we use unshift(),
// which is like push() but for the start, not end, of an array.
mapped.unshift(campaign.methods.requests(n).call());
}