You can do it like this:
function fillArray(value, len) {
if (len == 0) return [];
var a = [value];
while (a.length * 2 <= len) a = a.concat(a);
if (a.length < len) a = a.concat(a.slice(0, len - a.length));
return a;
}
It doubles the array in each iteration, so it can create a really large array with few iterations.
Note: You can also improve your function a lot by using push instead of concat, as concat will create a new array each iteration. Like this (shown just as an example of how you can work with arrays):
function fillArray(value, len) {
var arr = [];
for (var i = 0; i < len; i++) {
arr.push(value);
}
return arr;
}