Let's dive into the world of JavaScript microbenchmarks.

What is being tested?

MeasureThat.net is testing the performance of different methods for shallow cloning an array in JavaScript. Shallow cloning means creating a new copy of the array, but only copying the top-level elements (i.e., no recursive cloning). The test cases use a specific array arrayOf1kkNumbers with 100,000 elements.

Options being compared

The options being compared are:

1. concat: Using the Array.prototype.concat() method to create a new array.
2. spread: Using the spread operator (...) to create a new array.
3. slice: Using the Array.prototype.slice() method to create a new array.
4. Object.values: Using the Object.values() method to create an array from an object (although this is not strictly shallow cloning, as it uses the object's internal structure).
5. Array.from: Using the Array.from() constructor to create a new array.

Pros and cons of each approach

1. concat:
   • Pros: Simple and widely supported.
   • Cons: Creates a new copy of the entire original array, which can be slow for large arrays.
2. spread:
   • Pros: Fast and efficient, as it only copies the top-level elements.
   • Cons: Requires modern browsers that support the spread operator (introduced in ECMAScript 2015).
3. slice:
   • Pros: Efficient and widely supported, as it uses a optimized internal implementation.
   • Cons: Creates a new copy of the entire original array, which can be slow for large arrays.
4. Object.values:
   • Pros: Fast and efficient, as it only copies the top-level elements.
   • Cons: Not strictly shallow cloning, as it uses the object's internal structure.
5. Array.from:
   • Pros: Fast and efficient, as it only copies the top-level elements.
   • Cons: Requires modern browsers that support the Array.from() constructor (introduced in ECMAScript 2015).

Library usage

The test case using lodash is 5. Object values. The Object.values() method is a part of the Lodash library, which provides various utility functions for JavaScript.

Special JS features or syntax

There are no special JS features or syntax used in this benchmark. All tests use standard JavaScript and common array methods.

Other alternatives

If you want to implement your own shallow cloning algorithm, some other options include:

1. forEach: You can use the Array.prototype.forEach() method to iterate over each element of the original array and create a new copy.
2. map() + Array.prototype.slice(): You can use the Array.prototype.map() method to create a new array with cloned elements, followed by Array.prototype.slice() to remove the original array from memory.

Keep in mind that these alternatives may have different performance characteristics than the methods being tested in this benchmark.

I hope this explanation helps you understand what's going on in this JavaScript microbenchmark!