var arr = Array.from(Array(100).keys());
arr.slice(-1)[0];
arr[arr.length-1];
--enable-precise-memory-info
flag.
Test case name | Result |
---|---|
`Array.slice(-1)[0]` | |
`Array[Array.length]` |
Test name | Executions per second |
---|---|
`Array.slice(-1)[0]` | 10328980.0 Ops/sec |
`Array[Array.length]` | 7843144.0 Ops/sec |
Let's break down the provided benchmark and explain what's being tested, compared, and analyzed.
Benchmark Overview
The benchmark is comparing two ways to access the last element of an array in JavaScript: Array.slice(-1)[0]
and arr[arr.length-1]
.
Script Preparation Code
Before running each test case, the script preparation code creates a large array (arr
) with 100 elements, using the following line:
var arr = Array.from(Array(100).keys());
This creates an array of numbers from 0 to 99.
Benchmark Definition
The benchmark definition is a JSON object that contains two test cases:
Array.slice(-1)[0];
: This test case measures the performance of accessing the last element of the array using the slice()
method and indexing [0]
.arr[arr.length-1];
: This test case measures the performance of accessing the last element of the array directly using indexing [arr.length-1]
.Library/Features Used
In this benchmark, no libraries or special JavaScript features are used.
Options Compared
The two options being compared are:
Array.slice(-1)[0]
: This method creates a new slice of the original array with only one element (the last one), and then accesses that element using [0]
. This approach is often considered more explicit and safer, but may incur a performance overhead due to the creation of a new slice.arr[arr.length-1]
: This method directly indexes into the original array to access the last element. This approach is often considered faster and more efficient, as it avoids creating unnecessary intermediate data structures.Pros and Cons
Here are some pros and cons of each approach:
Array.slice(-1)[0]
:arr[arr.length-1]
:Other Alternatives
If you need to access the last element of an array in JavaScript, other alternatives include:
arr[arr.length - 1]
: This is a more concise way to access the last element using direct indexing.last()
that can be used to access the last element of an array.Benchmark Result
The latest benchmark result shows the performance metrics for both test cases:
Test Name | ExecutionsPerSecond |
---|---|
Array.slice(-1)[0] |
10328980.0 |
arr[arr.length-1] |
7843144.0 |
This suggests that accessing the last element using arr[arr.length-1]
is faster than using Array.slice(-1)[0]
. However, the actual performance difference may vary depending on the specific use case and JavaScript engine being used.
I hope this explanation helps!