Let's break down the benchmark definition and test cases to understand what is being tested.

Benchmark Definition:

The benchmark measures the performance difference between two approaches:

1. arr1.concat(arr2)
2. [ ...arr1, ...arr2 ] (using the ES6 spread operator)

These two approaches are used to concatenate two arrays, arr1 and arr2. The main difference between them is how they handle the resulting array.

Pros and Cons of each approach:

1. arr1.concat(arr2)
   • Pros:
     • Wide browser support (not specific to modern browsers)
     • Easy to understand and implement
   • Cons:
     • Creates a new, shallow copy of arr1, which can lead to unnecessary memory allocations.
     • May be slower than the spread operator due to its overhead.
2. [ ...arr1, ...arr2 ] (using ES6 spread operator)
   • Pros:
     • More efficient than concat() as it only creates a new array reference without creating a copy of the original arrays.
     • Faster execution time due to its optimized implementation in modern browsers.
   • Cons:
     • Requires modern browser support (ES6+).
     • May require additional setup or transpilation for older browsers.

Library:

In this benchmark, there is no explicit library mentioned. However, the use of ES6 spread operator ([ ...arr1, ...arr2 ]) implies that the benchmark is using a modern JavaScript engine with ES6 support.

Special JS feature/syntax:

The benchmark uses the ES6 spread operator ([ ...arr1, ...arr2 ]), which is a modern JavaScript syntax introduced in ECMAScript 2015. This syntax allows for concise array creation by expanding arrays or iterables.

Other alternatives:

For concatenating two arrays, other approaches include:

• arr1.push(...arr2): This approach modifies the original arr1 and can be slower due to its mutability.
• Array.prototype.slice().concat(arr2): This approach creates a shallow copy of arr1 using slice() and then concatenates arr2.

These alternatives may have different performance characteristics, depending on the specific use case and browser support.

Benchmark Preparation Code:

The provided preparation code sets up two arrays, arr1 and arr2, with three elements each. This allows for a straightforward test of the concatenation methods.

Latest Benchmark Result:

The latest benchmark result shows that Chrome 79 on Windows Desktop achieved:

• 1813151 executions per second using ES6 spread operator ([ ...arr1, ...arr2 ])
• 1028234 executions per second using arr1.concat(arr2)

This suggests that the ES6 spread operator outperforms the traditional concat() method in this specific benchmark.