I'd be happy to help explain the JavaScript microbenchmark on MeasureThat.net.

Benchmark Overview

The benchmark measures the performance of three different approaches for extending an array in JavaScript:

1. forEach loop with push
2. Spread operator (...) with push
3. Array spread operator ([...y, ...x])

Approaches and their pros/cons

1. forEach loop with push

This approach iterates over the array using a forEach loop and pushes each element to a new array.

Pros:

• Simple and easy to understand
• Works well for small arrays

Cons:

• Can be slow for large arrays due to the overhead of the forEach loop
• Creates a new array, which can lead to memory allocation issues if the original array is large

2. Spread operator (...) with push

This approach uses the spread operator to create a new array by spreading the elements of the original array into a new array.

Pros:

• Faster than the forEach loop approach
• More efficient than creating a new array from scratch

Cons:

• Requires support for the spread operator (introduced in ECMAScript 2015)
• May have performance implications if the original array is very large

3. Array spread operator ([...y, ...x])

This approach uses the array spread operator to create a new array by spreading the elements of both arrays into one.

Pros:

• Fast and efficient
• Does not require creating a new array from scratch

Cons:

• Requires support for the array spread operator (introduced in ECMAScript 2015)
• May have performance implications if the original arrays are very large

Library and Special JS Features

There is no library mentioned in the benchmark. However, it's worth noting that some browsers may use specialized JavaScript engines or optimizations that can affect the results of the benchmark.

None of the approaches rely on any special JavaScript features beyond the standard forEach loop and array spread operators.

Other Alternatives

If you need to extend an array, there are other approaches you could consider:

• Using a library like Lodash's each function
• Using a specialized array extension function (e.g., Array.prototype.pushAll)
• Using a different data structure altogether (e.g., using a linked list or a more efficient data structure for large arrays)

Keep in mind that the best approach will depend on your specific use case and requirements. The MeasureThat.net benchmark provides a useful starting point, but you may need to experiment with different approaches to find the one that works best for your needs.