Just move "var numbers = []"" inside the function. It's better to use let/const instead var.
Anyway I'm not sure why declaration outside the function doesn't work well, but the thing is that console.log(numbers) shows quite strange results in the Output

For JS If you need to know the inputs just add console.log to your code.
For example:
function testFunction(values){
console.log(values)
...you code...
return ...
}