function product(x) {
    let value = 1;
    for (let i = 0; i < x.length; i++) {
        value *= x[i];
    }
    return value;
}
The [product](https://en.wikipedia.org/wiki/Product_(mathematics)) of an array
is the result of multiplying all numbers together, starting using one as the multiplicative identity.

This runs in `O(n)`, linear time, with respect to the length of the array.

@param {Array<number>} x input
@return {number} product of all input numbers
@example
product([1, 2, 3, 4]); // => 24