Benchmark: array length effect

Script Preparation code:

var arr = [];
var count = 1000;
for (var i = 0; i < count; i++) {
    arr.push(i);
}
var arrLen = arr.length;

Tests:

cached
var sum=0; for (var i = 0; i < arrLen; i++){ sum = arr[i]; }
non-cached
var sum = 0; for (var i = 0; i < arr.length; i++){ sum = arr[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
cached
non-cached

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.3 Safari/605.1.15

Browser/OS: Safari 16 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
cached	18186.8 Ops/sec
non-cached	18090.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into explaining the provided JSON benchmark.

**Benchmark Overview**

The provided JSON represents a microbenchmark test case on MeasureThat.net, which measures the performance of JavaScript in different scenarios. The test compares two approaches to access an array element: with and without caching the array length.

**Script Preparation Code**

The script preparation code is as follows:
```javascript
var arr = [];
var count = 1000;
for (var i = 0; i < count; i++) {
    arr.push(i);
}
var arrLen = arr.length;
```
This code initializes an empty array `arr` and populates it with 1000 elements using a `for` loop. The length of the array is then stored in the variable `arrLen`.

**Html Preparation Code**

There is no HTML preparation code provided, which means that the test case does not involve any HTML-related setup.

**Benchmark Test Cases**

The benchmark consists of two individual test cases:

1. **cached**: This test case uses cached array length (`arrLen`) to access an element in the `arr` array.
```javascript
var sum = 0;
for (var i = 0; i < arrLen; i++) {
    sum = arr[i];
}
```
The `arrLen` variable is already calculated and stored in memory, so accessing its value does not require a dynamic lookup. This test case likely has better performance compared to the non-cached variant.

2. **non-cached**: This test case uses dynamic array length (`arr.length`) to access an element in the `arr` array.
```javascript
var sum = 0;
for (var i = 0; i < arr.length; i++) {
    sum = arr[i];
}
```
In this test case, `arr.length` is calculated on each iteration of the loop, which means that the length of the array needs to be looked up every time. This approach likely has poorer performance compared to the cached variant.

**Library and Purpose**

The provided benchmark does not use any libraries explicitly. However, it relies on built-in JavaScript features like dynamic arrays (`arr`), loops, and variable declarations.

**Special JS Feature or Syntax**

There are no special JavaScript features or syntax used in this benchmark. It only uses standard JavaScript constructs and techniques.

**Pros and Cons of Different Approaches**

The main difference between the two test cases is how the array length is accessed:

* **Cached**: This approach has better performance because `arrLen` is already calculated and stored in memory, reducing the number of dynamic lookups required.
* **Non-cached**: This approach has poorer performance because `arr.length` needs to be looked up every time, which can lead to additional overhead.

**Other Alternatives**

While MeasureThat.net provides this benchmark, other alternatives for measuring JavaScript performance include:

* Browser-specific benchmarks like those provided by browser vendors (e.g., Google Chrome DevTools)
* Online benchmarks like jsperf or Benchmark.js
* Local benchmarking tools like Node.js's `Benchmark` module

Keep in mind that the choice of benchmarking tool or platform depends on your specific needs, target audience, and performance requirements.

Related benchmarks:

array length effect (version: 0)

Comparing performance of: cached vs non-cached

Created: one year ago by: Guest

Jump to the latest result

cached

non-cached

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):