Overview

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided JSON represents a benchmark test case, which compares two approaches for accessing the last element of an array in JavaScript: using square bracket notation (array[0]) versus Array.prototype.at(0).

Benchmark Definition

The benchmark definition is:

• Script Preparation Code: "var data = [...Array(100000).keys()]"
  • This code creates a large array with 100,000 elements and assigns it to the variable data. The keys of this array are generated using the spread operator (...) and the Array constructor.
• Html Preparation Code: null
  • There is no HTML preparation code provided, which means that the benchmark only runs in a JavaScript environment.

Individual Test Cases

The benchmark consists of two test cases:

1. Test Case 1:
   • Benchmark Definition: "var d = data[data.length - 1]"
   • This line accesses the last element of the data array using square bracket notation (array[0]).
2. Test Case 2:
   • Benchmark Definition: "var z = data.at(-1)"
   • This line attempts to access the last element of the data array using the Array.prototype.at() method.

Pros and Cons

• Square Bracket Notation (array[0]):
  • Pros:
    • Wide support across older browsers and environments.
    • Easy to read and understand.
  • Cons:
    • Can be slower than the Array.prototype.at() method due to its nature of accessing elements at a specific index, even if the array is not fully populated.
• Array.prototype.at(0) Method:
  • Pros:
    • Generally faster and more efficient than square bracket notation for large arrays.
    • Provides a concise way to access the last element of an array without having to calculate the index manually.
  • Cons:
    • Limited support across older browsers and environments. (Added in ECMAScript 2019)
    • Requires modern JavaScript engines to execute.

Library/Functionality

• Array.prototype.at() Method:
  • This method is a part of the ECMAScript standard, introduced in ECMAScript 2019.
  • It provides an efficient way to access the element at a specific index in an array, even if the array is not fully populated.

Special JS Feature/Syntax

• No special JavaScript features or syntax are used in this benchmark.

Other Alternatives

For accessing the last element of an array, other alternatives include:

• Using Math.max() and the spread operator (...): var d = Math.max(...data)
• Using a loop to iterate through the elements of the array: var d; for (const i of data) { d = i; break; }

However, these alternatives may not be as efficient or concise as using square bracket notation (array[0]) or the Array.prototype.at() method.

Benchmark Preparation Code

The provided benchmark preparation code creates a large array with 100,000 elements and assigns it to the variable data. This ensures that both test cases have access to a large dataset for comparison.