Benchmark: For loop inline array.length vs captured variable

Script Preparation code:

var a = [];
for (var i = 0; i < 1000; i++) {
  a.push(Math.random());
}

Tests:

Inline
for (var i = 0; i < a.length; i++) { a[i] = a[i] * Math.random(); }
Captured
for (var i = 0, ilen = a.length; i < ilen; i++) { a[i] = a[i] * Math.random(); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Inline
Captured

Fastest: N/A

Slowest: N/A

Latest run results:

No previous 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 benchmark being tested is about comparing two approaches to iterating over an array in JavaScript: using `inline array.length` and capturing the length of the array into a separate variable (`captured variable`). The test checks which approach is faster for performing a simple operation on each element of the array (in this case, multiplying by a random number).

**Approach 1: Inline array.length**

In this approach, the length of the array is accessed directly within the loop using `a.length`. This means that every time through the loop, the value of `a.length` needs to be reevaluated.

Pros:

* Simple and straightforward implementation.
* No additional memory usage or variables are required.

Cons:

* Repeatedly accessing `a.length` can lead to slower performance due to the overhead of reevaluating its value on every iteration.

**Approach 2: Captured variable**

In this approach, the length of the array is stored in a separate variable (`ilen`) before the loop. This allows the length to be accessed only once during the initialization phase, avoiding the need for repeated reevaluations.

Pros:

* Avoids the overhead of reevaluating `a.length` on every iteration.
* Can potentially lead to better performance due to reduced loop overhead.

Cons:

* Requires additional memory usage and variable setup (assigning a new value to `ilen`).
* May introduce some extra computation time for initializing the loop variable.

**Library Used: None**

There is no explicit library mentioned in this benchmark. However, it's worth noting that the use of JavaScript arrays and loops is a fundamental aspect of JavaScript programming, and most libraries or frameworks build upon these basic constructs.

**Special JS Features/Syntax: None**

This benchmark does not utilize any special JavaScript features or syntax beyond standard array operations and loops.

**Other Alternatives**

Some alternative approaches to iterating over arrays in JavaScript include:

* Using `for...of` loops (introduced in ES6), which eliminate the need for explicit loop variables and indexing.
* Using `Array.prototype.forEach()` or `Array.prototype.map()`, which provide higher-level, more functional programming approaches to array iteration.

While these alternatives might not be directly applicable to this specific benchmark, they demonstrate some of the evolving features and paradigms in modern JavaScript development.

Related benchmarks:

For loop inline array.length vs captured variable (version: 0)

Comparing performance of: Inline vs Captured

Created: 9 years ago by: Guest

Jump to the latest result

Inline

Captured

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):