Benchmark: findLastItem - MeasureThat.net

Script Preparation code:

var arr = ['1', '2', '3', '1', '2', '3', '1', '2', '3'];

Tests:

reverse&find
const foundling = arr.reverse().find(item => item === '2');
filter&pop
const foundling = arr.filter(item => item === '2').pop();
filter&lastIndex
const filteredArr = arr.filter(item => item === '2'); const foundling = filteredArr[filteredArr.length - 1];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
reverse&find
filter&pop
filter&lastIndex

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explain what's being tested.

**Benchmark Definition**

The provided JSON defines a benchmark named "findLastItem". The script preparation code creates an array `arr` with some sample data, and there are no additional HTML preparation codes specified.

**Script Preparation Code**
```javascript
var arr = ['1', '2', '3', '1', '2', '3', '1', '2', '3'];
```
This code defines an array `arr` containing some numbers with duplicates. The purpose of this array is likely to provide a baseline for the benchmark.

**Individual Test Cases**

The benchmark includes three individual test cases, each representing a different approach to find the last occurrence of a specific item in the array:

1. **reverse&find**
```javascript
const foundling = arr.reverse().find(item => item === '2');
```
This approach reverses the entire array and then uses the `find` method to locate the first occurrence of the item `'2'`.

2. **filter&pop**
```javascript
const foundling = arr.filter(item => item === '2').pop();
```
This approach filters the original array to only include items equal to `'2'`, and then uses the `pop` method to remove and return the last element of the filtered array.

3. **filter&lastIndex**
```javascript
const filteredArr = arr.filter(item => item === '2');
const foundling = filteredArr[filteredArr.length - 1];
```
This approach filters the original array, just like in the second test case, but then uses indexing (`[filteredArr.length - 1]`) to access and return the last element of the filtered array.

**Library and Special JS Features**

There are no libraries used in this benchmark. However, there is a special JavaScript feature being used: `const` declaration with type annotations (e.g., `item => item === '2'`). This syntax is part of modern JavaScript features introduced in ECMAScript 2015 (ES6).

**Pros and Cons**

Each approach has its pros and cons:

1. **reverse&find**: Pros - simple to implement, fast performance. Cons - reverses the entire array, which can be inefficient for large arrays.
2. **filter&pop**: Pros - efficient use of `filter` method, easy to understand. Cons - creates a new filtered array, which can consume extra memory.
3. **filter&lastIndex**: Pros - avoids creating a new filtered array, uses indexing, but may be slower due to the additional calculation.

**Other Alternatives**

Some alternative approaches to find the last occurrence of an item in an array include:

* Using `indexOf` method with negative index values (e.g., `-1 + arr.length`)
* Using a loop with a counter variable
* Using a library function like Lodash's `lastIndexOf`

Keep in mind that these alternatives may not be as efficient or readable as the approaches tested in this benchmark.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.107 Safari/537.36

Browser/OS: Chrome 92 on Windows

View result in a separate tab

Test name	Executions per second
reverse&find	4747897.5 Ops/sec
filter&pop	3753245.5 Ops/sec
filter&lastIndex	3135154.8 Ops/sec

Related benchmarks:

findLastItem (version: 1)

Comparing performance of: reverse&find vs filter&pop vs filter&lastIndex

Created: 3 years ago by: Registered User

Jump to the latest result

reverse&find

filter&pop

filter&lastIndex

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated one month ago):