Let's dive into the explanation.

Overview

The provided JSON represents a JavaScript microbenchmark test case on MeasureThat.net. The benchmark tests three approaches to removing duplicate elements from an array: using Lodash's uniqBy function, creating a new Set object, and spreading the Set object using the spread operator ([...]).

Tested Approaches

1. Lodash uniqBy: This approach uses the Lodash library's uniqBy function to remove duplicate elements from the array based on a custom comparison function.
2. Set: This approach creates a new Set object and adds each element of the original array to it. Since sets only store unique values, this approach removes duplicates automatically.
3. Set spread: This approach creates a new Set object and spreads its elements into an array using the spread operator ([...]). The resulting array will have duplicate elements removed.

Pros and Cons

1. Lodash uniqBy:
   • Pros: Customizable comparison function allows for fine-grained control over duplicate removal.
   • Cons: Requires Lodash library to be included, which may add unnecessary overhead.
2. Set:
   • Pros: Fast and efficient, as sets only store unique values.
   • Cons: Does not preserve the original array order, and may require additional processing to restore it.
3. Set spread:
   • Pros: Preserves the original array order and is relatively fast.
   • Cons: May be slower than using a Set object directly, as it involves creating an intermediate array.

Library: Lodash

Lodash (a library of functions for functional JavaScript programming) provides the uniqBy function, which removes duplicate elements from an array based on a custom comparison function. The comparison function is used to determine whether two elements are equal or not.

Special JS Feature/Syntax: Spread Operator ([...] )

The spread operator is used in the "Set spread" approach to create a new array by spreading the elements of the Set object. This syntax was introduced in ECMAScript 2015 (ES6) and allows for easy creation of arrays from other iterables, such as sets.

Other Alternatives

1. Array.prototype.filter(): Instead of using a Set object or Lodash's uniqBy function, you could use the filter() method to remove duplicate elements from an array.
2. Object.values() and Array.from(): If you need to preserve the original array order, you could use Object.values() to get the values of an object (which can be used as a set), followed by Array.from() to create an array from it.

Here's some sample code using these alternatives:

// Using filter()
var myArr = [...]; // your array
var myCopy = myArr.filter((val, index, self) => {
  return index === self.indexOf(val);
});

// Using Object.values() and Array.from()
var obj = { /* your object */ };
var myObjSet = new Set(Object.values(obj));
var myCopySpread = [...myObjSet];