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

Benchmark Definition: The benchmark is designed to compare three approaches for concatenating an array:

1. Push: Using the push() method to add elements to the end of the array.
2. Spread Operator (...): Utilizing the new ES6 spread operator to create a new array by copying and extending the original array.

Options Compared: The benchmark compares the performance of these two methods (Push and Spread Operator) for concatenating an array with a large size (2000000 elements, filled with 2). The Push method involves calling push() on the end of the array to add new elements, while the Spread Operator creates a new array by copying the original array's elements and adding a single element (1).

Pros and Cons:

• Push Method:
  • Pros:
    • Simple and widely supported.
    • Can be useful for modifying existing arrays.
  • Cons:
    • Can lead to performance issues when dealing with large arrays, as it requires multiple array allocations and resizing.
• Spread Operator (...):
  • Pros:
    • More concise and readable than the Push method.
    • Creates a new array without modifying the original one.
  • Cons:
    • May incur overhead due to creating a new array copy.

Library and Special JS Features: The benchmark uses no external libraries. However, it does utilize a JavaScript feature introduced in ECMAScript 2018 (ES2018): the spread operator (...). The spread operator allows for concise array creation by expanding an existing array or object into a new one.

Other Considerations:

• Array Allocation: When using the Push method, the browser needs to allocate new memory for each added element. This can lead to increased memory usage and slower performance.
• Cache Locality: Modern browsers use various caching mechanisms to improve performance. However, when concatenating arrays using the Push method, the cache locality is disrupted due to the frequent allocation of new memory.

Alternatives: In addition to the two methods being compared in this benchmark, other approaches for array concatenation exist:

• concat() Method: This is another widely supported method for concatenating arrays. While it may have similar performance characteristics to the Push method, its syntax can be less readable.
• array.prototype.reduce() Method: Some browsers support using reduce() to concatenate arrays. However, this approach often requires more code and can lead to less cache locality.

For a simple array concatenation task, the Spread Operator (...) is generally recommended due to its concise syntax and performance benefits.