Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

The provided JSON represents two test cases, each with its own benchmark definition. We'll break down what's being tested and explore the different approaches.

Benchmark Definition

The first section defines a benchmark between typeof undefined and === undefined. This is an interesting comparison because typeof returns a string describing the type of a variable ("undefined" in this case), whereas === checks for exact equality. In most JavaScript engines, these two values are not equal.

Script Preparation Code

The script preparation code defines a variable t with the value "not undefined". This is done to create a scenario where both conditions are true: typeof t returns "undefined", and t === undefined returns false.

Html Preparation Code

There's no HTML preparation code, so we'll focus on the script-level comparison.

Options compared

The two test cases compare the following options:

1. typeof: Returns a string describing the type of a variable ("undefined" in this case).
2. === undefined: Checks for exact equality with undefined.

Pros and Cons

• typeof:
  • Pros: Generally faster, as it's an optimized operation.
  • Cons: May not be equal to undefined due to type coercion or other quirks.
• === undefined:
  • Pros: Provides a clear indication of whether the variable is exactly equal to undefined.
  • Cons: May be slower, as it involves a more complex comparison.

In this specific case, since we're comparing typeof and === undefined, the difference in performance will likely be negligible. However, if you need to perform more complex type checks or equality comparisons, === undefined might be a better choice.

Library and purpose

There's no library mentioned in the provided code. The tests rely solely on JavaScript's built-in functionality.

Special JS feature or syntax

None are explicitly used or mentioned. However, it's worth noting that typeof and === undefined both rely on JavaScript's type coercion rules, which can sometimes lead to unexpected behavior if not considered carefully.

Other alternatives

If you need to compare other values, such as:

• value == value: This is essentially the same as === undefined, but without checking for strict equality.
• typeof value === 'undefined': This checks if the value is of type undefined, which might be useful in certain scenarios.

Keep in mind that these alternatives may have different performance characteristics and should be tested accordingly.