I'd be happy to explain what's being tested in the provided benchmark.

What is being tested?

The benchmark compares two approaches to create a new array by combining two existing arrays: using the spread operator ([...arr1, ...arr2]) and using Lodash's union function (_.union(arr1, arr2)).

Options compared

Two options are being compared:

1. Spread Operator: This method uses the ... operator to create a new array by spreading the elements of two arrays.
2. Lodash Union: This method uses the Lodash library's union function to create a new array containing all unique elements from two arrays.

Pros and Cons

Spread Operator:

Pros:

• Simple and concise syntax
• Fast execution, as it only involves a simple concatenation operation
• No additional dependencies required (built-in to JavaScript)

Cons:

• Can be slower than the Lodash approach for very large arrays, due to the overhead of creating a new array.
• May not perform well if the two input arrays are of different lengths.

Lodash Union:

Pros:

• Efficient and optimized implementation, which can outperform the spread operator for large arrays.
• Handles cases where the two input arrays have different lengths.

Cons:

• Requires an external library dependency (Lodash).
• More complex syntax than the spread operator.

Other considerations

Both approaches assume that the input arrays arr1 and arr2 are already created and contain elements to be combined. The benchmark uses JavaScript arrays as the input data structures.

Library: Lodash

The union function from Lodash is used in the benchmark, which provides a convenient way to combine arrays while ignoring duplicates.

Special JS feature or syntax (not applicable)

There are no special JavaScript features or syntaxes being tested in this benchmark.

Other alternatives

If you were to implement your own array union logic, you could consider using:

1. Array.prototype.concat(): A simple and straightforward approach that involves concatenating the two arrays.
2. Set data structure: Using sets can provide an efficient way to combine arrays by automatically eliminating duplicates.

Keep in mind that implementing these alternatives would likely be slower than using the Lodash union function or the spread operator, especially for large datasets.