Benchmark: Storing array length before for

Tests:

Without
const array = Array.from({length: 12}).fill(1); for(let i = 0; i < array.length; i++) { const a = i**2; }
With
const array = Array.from({length: 12}).fill(1); for(let i = 0, total = array.length; i < total; i++) { const a = i**2; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Without
With

Fastest: N/A

Slowest: N/A

Latest run results:

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

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Let's dive into the world of JavaScript microbenchmarks!

**Benchmark Overview**

The provided JSON represents a benchmark for measuring the performance difference between two approaches in storing array length before using it in a `for` loop.

**Script Preparation Code**

There is no script preparation code specified, which means that the test cases will be executed directly from the benchmark definition strings.

**Individual Test Cases**

We have two test cases:

1. **Without**
```javascript
const array = Array.from({length: 12}).fill(1);
for(let i = 0; i < array.length; i++) {
  const a = i**2;
}
```
In this case, the `array` length is accessed after the `for` loop has been defined.

2. **With**
```javascript
const array = Array.from({length: 12}).fill(1);
for(let i = 0, total = array.length; i < total; i++) {
  const a = i**2;
}
```
In this case, the `array` length is accessed before the `for` loop has been defined.

**Options Compared**

The two approaches are compared:

* **Without**: The array length is accessed after the `for` loop has been defined.
* **With**: The array length is accessed before the `for` loop has been defined.

**Pros and Cons**

### Without

Pros:

* Simplifies code by not requiring an extra variable to store the array length.
* May be more concise and easier to read for some developers.

Cons:

* Can lead to slower performance because the browser has to execute additional steps to calculate the array length, such as traversing the array's prototype chain.

### With

Pros:

* Avoids the overhead of calculating the array length after the `for` loop has been defined.
* May result in faster performance due to reduced computational overhead.

Cons:

* Requires an extra variable to store the array length, which can make the code slightly less readable for some developers.

**Library**

There is no library explicitly mentioned in the benchmark definition. However, it's likely that the `Array.from()` method is used, which is a part of the ECMAScript standard and not specific to any particular library. The `fill()` method is also a built-in JavaScript method.

**Special JS Feature or Syntax**

The test cases use the exponentiation operator (`**`) to calculate `i^2`, which is a new feature introduced in ECMAScript 2016 (ES6). This syntax was not available in previous versions of JavaScript. The presence of this feature may affect the compatibility of the benchmark across different browsers and environments.

**Other Alternatives**

If you're interested in exploring alternative approaches, here are some options:

* Use a library like `lodash` to calculate the array length, which can provide more efficient performance.
* Use a different data structure, such as an array-like object or a typed array, that provides faster access to its length.
* Experiment with different loop optimizations, such as using `for...of` loops instead of traditional `for...in` loops.
* Investigate the impact of caching and memoization on performance in this specific benchmark.

Keep in mind that these alternatives may require significant changes to your codebase or may not be applicable to this particular benchmark.

Related benchmarks:

Storing array length before for (version: 0)

Comparing performance of: Without vs With

Created: 4 years ago by: Guest

Jump to the latest result

Without

With

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):