Let's dive into the world of JavaScript microbenchmarks.

What is tested?

The provided benchmark tests four different approaches to empty an array in JavaScript:

1. Instantiating a new, empty array (arr1 = []).
2. Setting the length of an existing array to zero (arr2.length = 0).
3. Using the splice(0, arr3.length) method to remove all elements from an array (arr3.splice(0, arr3.length)).
4. Popping all values from an array using a while loop (while(arr4.length > 0){ arr4.pop();}).

Options comparison

Here's a brief overview of each approach and its pros and cons:

1. Instantiating a new array: This method is simple and efficient, as it involves creating a new object and assigning it to the variable arr1. However, it requires more memory allocation compared to other methods.
2. Setting length to zero: This method is also straightforward and doesn't require any additional memory allocation. However, it can be slower than instantiating a new array because it needs to update the internal length property of the array object.
3. Splice: Using splice(0, arr3.length) removes all elements from the array by updating the internal length property. This method is similar to setting the length to zero but uses a different API. It can be slower than instantiating a new array because it needs to perform additional operations on the array object.
4. Pop all values: Using a while loop to pop all values from an array is the most memory-intensive approach, as it involves repeatedly calling the pop() method and discarding the returned value.

Library usage

None of the provided benchmark definitions uses any external libraries or frameworks.

Special JS feature or syntax

There are no special JavaScript features or syntax used in these benchmark definitions. The code is written in plain JavaScript and follows standard syntax and semantics.

Other alternatives

If you're interested in exploring alternative approaches to emptying an array, here are a few more options:

• Using fill() method: arr5.fill(0); would clear the array by filling it with zeros.
• Using map() method with an identity function: arr6.map(() => 0); would create a new array with all elements set to zero and then discard the original array.
• Using reduce() method with an identity function: arr7.reduce((a, b) => a + b, 0); would create a new array with the sum of all elements and then discard the original array.

Keep in mind that these alternatives may have different performance characteristics compared to the original benchmark definitions.