I'd be happy to help you understand the JavaScript microbenchmark on MeasureThat.net.

What is being tested?

The benchmark is testing two different approaches to check if variables B and C are undefined:

1. Using typeof B === 'undefined' || typeof C === 'undefined'
2. Using [typeof B, typeof C].every(function(elem) { return elem === 'undefined'; })

Options being compared

The two options are comparing the performance of checking if variables are undefined using a simple typeof check versus an array-based check.

Pros and Cons

1. Simple typeof check: This approach is concise and easy to read, but it may not be as efficient as other methods. It relies on the fact that undefined is a primitive value in JavaScript.
2. Array-based check: This approach creates an array with the results of typeof B and typeof C, and then uses the every() method to check if all elements are equal to 'undefined'. This approach can be more efficient for larger arrays, but it may be less readable due to its use of a functional programming style.

Other considerations

• The benchmark is running on a Chrome 53 browser with an Intel Mac OS X 10_11_6 machine.
• The array group test uses the latest JavaScript features, including template literals and the every() method.

Library used

There is no library being used in this benchmark. However, it's worth noting that some browsers may have built-in optimizations for certain types of checks (e.g., typeof) or may use libraries like V8 (used by Chrome) to execute JavaScript code.

Special JS features

The array group test uses a few special JavaScript features:

• Template literals ([...].every(function(elem) { ... }))
• The every() method
• Arrow functions (=> ...)

These features are relatively modern and may not be supported in older browsers or environments.

Other alternatives

If you're interested in exploring alternative approaches to this benchmark, here are a few options:

• Use a different type of check (e.g., !!B !== !!C)
• Compare the performance of using in operator instead of typeof
• Test the performance of using a custom implementation for checking if variables are undefined
• Compare the performance of using a JavaScript library like Lodash or Ramda to perform checks

Keep in mind that these alternatives may not be relevant to the specific use case being benchmarked, and the results may vary depending on the environment and browser being used.