Let's dive into the explanation of the provided benchmark.

What is tested?

The benchmark tests two approaches for concatenating two arrays: Array.prototype.concat and the spread operator ([ ...a, ...b ]). The goal is to compare their performance in JavaScript microbenchmarks.

Options compared

Two options are being compared:

1. Array.prototype.concat: A traditional method for concatenating arrays, which was part of the ECMAScript standard before the introduction of the spread operator.
2. Spread operator ([ ...a, ...b ]): A new syntax introduced in ECMAScript 2015 (ES6) that allows creating a new array by spreading elements from existing arrays.

Pros and cons of each approach

1. Array.prototype.concat:
   • Pros:
     • Widely supported and well-established.
     • Can be used with older browsers or environments that don't support the spread operator.
   • Cons:
     • May have performance overhead due to the function call and array creation.
2. Spread operator ([ ...a, ...b ]):
   • Pros:
     • More concise and expressive syntax.
     • Can be faster than concat because it avoids the function call overhead.
   • Cons:
     • Requires ECMAScript 2015 support (ES6+) for older browsers or environments.

Library usage

In this benchmark, there is no explicit library usage mentioned. However, the spread operator syntax relies on the Array.prototype object and the ... spread syntax, which are built-in JavaScript features.

Special JS feature/syntax

The spread operator ([ ...a, ...b ]) uses a new syntax introduced in ECMAScript 2015 (ES6). This syntax is not mentioned in older browsers or environments that don't support ES6+.