Let's break down the provided benchmark and its options.

The benchmark compares two approaches to concatenate strings in JavaScript:

1. Array.join(): This method takes an array of values as input and concatenates them together with a separator (in this case, a space).
2. Template literal (${expression}...): This is a feature introduced in ECMAScript 2015 (ES6) that allows you to embed expressions inside template literals.

Let's examine the pros and cons of each approach:

Array.join():

Pros:

• Widely supported across browsers
• Can handle arrays with multiple elements

Cons:

• May be slower due to the overhead of calling a function on an array
• Less readable than template literals for simple concatenations
• Does not provide a way to escape special characters (e.g., \n)

Template literal:

Pros:

• More expressive and readable than join()
• Provides a way to escape special characters using the ${expression} syntax (e.g., ${hello}\n${world})
• Faster execution due to the compilation of template literals

Cons:

• Not supported in older browsers (pre-ES6)
• May require additional setup for certain use cases (e.g., transpiling to an older JavaScript version)

The benchmark uses Chrome 104 on a Mac OS X system to compare these two approaches. The results show that the template literal approach outperforms join().

Other alternatives include:

• String.prototype.concat(): This method concatenates two or more strings together, but it's less readable and may be slower than template literals.
• String.replace(): This method can be used to concatenate strings by replacing a placeholder with the actual string value. However, this approach is less efficient and more complex than template literals.

The library mentioned in the benchmark preparation code is not explicitly stated, as the script preparation code does not include any external libraries. However, it's worth noting that some browsers may include additional libraries or modules when running JavaScript benchmarks.

As for special JS features or syntax, there are a few aspects to note:

• Arrow functions: While arrow functions are used in the benchmark (e.g., const foo = () => [hello, world].join(' - ')), they are not explicitly mentioned as a distinct feature.
• Promises and async/await: There is no evidence of promises or async/await being used in this specific benchmark.

I hope this explanation helps you understand the benchmark and its options!