I'll break down the benchmark and explain what's being tested, compared options, pros and cons of those approaches, library usage, special JavaScript features or syntax, and other considerations.

Benchmark Overview

The benchmark tests two alternatives for checking if an array is an instance of the Array constructor:

1. _ (the underscore function) from the Underscore.js library
2. Array.isArray() (a built-in JavaScript method)

Script Preparation Code

The script preparation code creates a large array a with 100 elements, each containing a string value "val${i}", where i is an index.

var a = [];
for (var i = 0; i < 100; i++) {
    a[i] = 'val' + i;
}

Html Preparation Code

The HTML preparation code includes a reference to the Underscore.js library, which provides the _ function used in the benchmark.

<script src='https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js'></script>

Test Cases

There are two test cases:

1. _.isArray(a);
2. Array.isArray(a);

Both test cases create an array a and pass it to the respective function.

Library Usage - Underscore.js

Underscore.js is a popular JavaScript utility library that provides a concise way to perform common tasks, such as iterating over arrays or strings, creating functions, and more. The _ function in this benchmark is used to check if an array is an instance of the Array constructor.

Comparison Options

The two options being compared are:

1. _.isArray(a);
2. Array.isArray(a);

Pros and Cons of Each Approach:

_ (Underscore.js)

Pros:

• Often faster than Array.isArray() because it can use native JavaScript methods under the hood.
• Can provide more flexible and concise way to perform array checks in certain scenarios.

Cons:

• Requires an additional library download (Underscore.js) and potential additional overhead due to its functionality.
• May not be as widely adopted or understood as the built-in Array.isArray() method.

Array.isArray()

Pros:

• Built into modern JavaScript engines, eliminating the need for a separate library.
• Widely supported and well-documented, making it easier to understand and use.
• Generally faster than using an external library like Underscore.js.

Cons:

• May not provide as concise or flexible way to perform array checks in certain scenarios.
• Can be slower than _.isArray() if optimized native methods are used under the hood.

Other Considerations

• The benchmark results show that Chrome 83, running on a Windows Desktop, favors Array.isArray(), while another instance runs faster with _.isArray(a);.
• These results may not generalize to other browsers, environments, or performance profiles.
• The choice between these two approaches ultimately depends on the specific requirements and constraints of your application.

Alternatives

If you don't want to use a third-party library like Underscore.js, you can implement an array check function similar to Array.isArray() using native JavaScript methods. For example:

function isArray(arr) {
    return arr instanceof Array && arr.constructor === Array;
}

Alternatively, you could explore other libraries or implementations that provide alternative array check functions.

Keep in mind that the choice of implementation ultimately depends on your specific use case and performance requirements.