Let's break down the provided benchmark and its test cases.

Overview

The benchmark is designed to compare the performance of three approaches for removing duplicates from an array: Lodash's union function, creating a new Set using the spread operator (new Set([...a, ...b])), and Lodash's uniq function with the spread operator (_.uniq([...a, ...b])). The benchmark aims to determine which approach is the most efficient.

Test Cases

There are three test cases:

1. Lodash union: This test case uses Lodash's union function to combine two arrays and remove duplicates.
2. New Set: This test case creates a new Set by spreading two arrays together, effectively removing duplicates.
3. Lodash uniq spread: This test case uses Lodash's uniq function with the spread operator to remove duplicates from an array.

Options Compared

The benchmark is comparing three options:

1. Lodash's union function
2. Creating a new Set using the spread operator (new Set([...a, ...b]))
3. Lodash's uniq function with the spread operator (_.uniq([...a, ...b]))

Pros and Cons

Here are some pros and cons of each approach:

1. Lodash union:
   • Pros: Easy to use, well-tested library.
   • Cons: May have a performance overhead due to the complexity of the function.
2. New Set:
   • Pros: Simple, efficient, and widely supported.
   • Cons: Requires modern JavaScript versions (ECMAScript 2015+) and may not work in older browsers.
3. Lodash uniq spread:
   • Pros: Simple, efficient, and well-tested library.
   • Cons: May have a performance overhead due to the spread operator.

Libraries

Two libraries are used in this benchmark:

1. Lodash (version 4.17.5): A popular JavaScript utility library that provides various functions for data manipulation and more.
2. No other libraries are used in the test cases.

Special JS Features or Syntax

The benchmark uses modern JavaScript features, such as:

1. Spread operator ([...a, ...b])
2. Rest parameters ( implicit, not explicit)
3. ES6 classes (not used explicitly, but JavaScript version is 2015+, which requires ES6 compatibility)

Overall, the benchmark provides a good comparison of three approaches for removing duplicates from an array and highlights the pros and cons of each approach.

Other Alternatives

If you're looking for alternative ways to remove duplicates from an array, here are some options:

1. Use Array.prototype.filter(): a.filter((x, i) => a.indexOf(x) === i)
2. Use Array.prototype.reduce(): a.reduce((acc, x) => acc.includes(x) ? acc : [...acc, x])
3. Use Set objects: new Set(a).size
4. Use JSON.parse(JSON.stringify([...a, ...b])): This approach assumes that the elements in the array are JSON serializable.

Keep in mind that each of these alternatives has its own trade-offs and may not be as efficient or easy to use as the approaches tested in this benchmark.