Let's break down the provided benchmark.

What is tested?

The benchmark tests three different approaches to concatenate two arrays:

1. Array.prototype.concat(): The traditional method for concatenating arrays in JavaScript.
2. Spread operator (...): The new ES6 syntax for spreading array elements into a new array.
3. Lodash's merge() function: A utility function from the popular JavaScript library Lodash that merges two or more arrays into one.

Options compared

The benchmark compares these three approaches on an immutable data requirement, creating fresh arrays for each case.

Pros and Cons of each approach

1. Array.prototype.concat():
   • Pros: Simple, widely supported, and has been the standard way to concatenate arrays in JavaScript for a long time.
   • Cons: Creates a new array, which can lead to performance issues if dealing with large datasets or when memory is limited.
2. Spread operator (...)
   • Pros: Creates a shallow copy of the original array, which is more efficient than concat() for large arrays. Also, it's a concise and expressive way to concatenate arrays.
   • Cons: Requires modern JavaScript versions (ES6+) and may not work in older browsers or environments that don't support ES6 syntax.
3. Lodash's merge() function:
   • Pros: Provides a standardized and efficient way to merge arrays, which can be useful in various use cases. It also offers more features than just concatenation, such as merging objects.
   • Cons: Requires including the Lodash library in your project, which may add unnecessary size and complexity.

Library and purpose

Lodash is a popular JavaScript utility library that provides a comprehensive set of functions for various tasks, such as array manipulation, string manipulation, and more. The merge() function in particular is designed to merge two or more arrays into one, handling edge cases like null or undefined values.

Special JS feature or syntax

There's no specific special JS feature or syntax used in this benchmark apart from the use of ES6 spread operator (...), which requires modern JavaScript versions. However, it's worth noting that Lodash is a popular library and using its functions can provide a standardized way to perform common tasks.

Other alternatives

If you don't want to use the spread operator or Lodash's merge() function, you could consider other approaches:

• Using the concat() method with a loop: var other = []; while (array1.length > 0) { other.push(array1.shift()); if (array2.length > 0) { other.push(array2.shift()); } }
• Using array literals and push(): var other = [array1, array2];

However, these alternatives are generally less efficient than the spread operator or Lodash's merge() function.

In summary, the benchmark provides a useful comparison of three approaches to concatenate arrays in JavaScript: traditional concat(), modern spread operator, and standardized Lodash merge() function.