Benchmark: For with and without external variables

Script Preparation code:

var arr = [];
for (var i = 0; i < 100000; i++) {
  arr.push({
    Number: i
  });
};

var e = null;
var f = null;

function doWork(o, i) {
  e = o;
};

Tests:

1
for (var i = 0, len = arr.length; i <= len; i++) { e = arr[i]; };
2
var i = 0; var len = arr.length; for (; i <= len; i++) { f = arr[i]; };

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
1
2

Fastest: N/A

Slowest: N/A

Latest run results:

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

LLMs can make mistakes. Check important info.

I'll do my best to explain the provided benchmark and its results in a way that's easy to understand for software engineers of various skill levels.

**Benchmark Overview**

The provided benchmark is designed to measure the performance difference between two approaches when iterating over an array in JavaScript. The benchmark consists of two test cases:

1. **Test Case 1**: Uses a traditional `for` loop with a variable (`i`) that increments from 0 to the length of the array.
2. **Test Case 2**: Uses a `for` loop with a counter (`i`) that increments from 0 to the length of the array, but uses the array's `length` property to access elements.

**Script Preparation Code**

The script preparation code sets up an array `arr` with 100,000 elements, each containing a single property `Number` initialized with the index value. It also declares two variables `e` and `f`, which are used as test data in the benchmark.

**Html Preparation Code**

There is no HTML preparation code provided, suggesting that this is a headless browser or server-side benchmarking scenario.

**Library Usage**

In neither of the two test cases does the benchmark explicitly use any external libraries. However, it's worth noting that Chrome 59, which appears in both benchmark results, uses the V8 JavaScript engine, which is a popular open-source JavaScript engine used by Google.

**Special JS Features or Syntax**

Neither of the two test cases employs any special JavaScript features or syntax beyond standard `for` loops and array access. However, it's essential to be aware that the use of `var` instead of `let` or `const` can introduce issues with variable scoping and hoisting.

**Benchmark Results**

The benchmark results show the execution rate (`ExecutionsPerSecond`) for each test case on a device running Chrome 59 on Linux. The results are:

* **Test Case 1**: 41.411766052246094 executions per second
* **Test Case 2**: 41.19850158691406 executions per second

These results suggest that, in this specific scenario, there is no significant performance difference between using a traditional `for` loop with a variable and a `for` loop with an array's `length` property.

**Other Alternatives**

When benchmarking JavaScript performance, it's essential to consider the following alternatives:

1. **Modern JavaScript engines**: Other popular JavaScript engines like SpiderMonkey (Firefox) or SquirrelFish (Safari) might behave differently in this scenario.
2. **Different iteration methods**: Consider using `forEach`, `map`, or `filter` instead of traditional loops for a more modern and efficient approach.
3. **Array initialization**: Use `new Array(100000)` or `Array.from({ length: 100000 })` to create the array, as this can affect performance due to memory allocation overhead.

Keep in mind that the results may vary depending on the specific use case and requirements of your application.

Overall, while there is a small difference in execution rate between the two test cases, it's essential to consider the context and potential variations in performance when making decisions about your JavaScript code.

Related benchmarks:

For with and without external variables (version: 0)

Comparing performance of: 1 vs 2

Created: 8 years ago by: Guest

Jump to the latest result

1

2

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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