Benchmark: Array loop with cached length

Script Preparation code:

var arr = [];

for( var cpt = 0; cpt < 1000; cpt++ ) {
  arr.push( Math.random() );
}

var someFn = function( item ) {
  return item * 3 + item / 5;
}

Tests:

With length caching
for( var i = 0, n = arr.length; i < n; i++ ) { someFn( arr[ i ] ); }
Without length caching
for( var i = 0; i < arr.length; i++ ) { someFn( arr[ i ] ); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
With length caching
Without length caching

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'd be happy to explain what's tested in the provided JSON benchmark.

**Benchmark Overview**

The benchmark measures the performance of JavaScript loops with and without caching the array length. The goal is to compare how much faster one approach is compared to another, which can help identify optimizations for better performance.

**Script Preparation Code**

The script preparation code creates an empty array `arr` and then populates it with 1000 random values using a loop. It also defines a function `someFn` that takes an item as input, multiplies it by 3, and divides it by 5, returning the result.

**Test Cases**

There are two test cases:

1. **With length caching**: The benchmark definition uses the loop variable `i` to iterate over the array, but also accesses the `length` property of the array object to check if the loop has reached its end. This approach caches the length of the array once at the beginning of the loop, reducing the number of times it needs to access the `length` property.
2. **Without length caching**: The benchmark definition uses a simple loop that increments the variable `i` until it reaches the length of the array. In this case, the `length` property is accessed every iteration.

**Options Compared**

The two test cases compare the performance of loops with and without caching the array length. This allows us to see which approach is faster.

**Pros and Cons**

* **With length caching**: Pros:
	+ Reduces the number of times the `length` property needs to be accessed, reducing overhead.
	+ Can be slightly faster due to reduced branching.
* Cons:
	+ Requires additional memory access (cache) to store the length value.
* **Without length caching**: Pros:
	+ Does not require any additional memory access.
	+ Is simpler and more straightforward.
Cons:
	+ Requires more iterations over the `length` property, increasing overhead.

**Library**

There is no explicit library used in this benchmark. However, some JavaScript engines (like V8) may optimize loops with caching using internal data structures or algorithms that are not exposed through public APIs.

**Special JS Feature/Syntax**

There is no special JavaScript feature or syntax used in this benchmark.

**Alternatives**

Other alternatives to measure loop performance could include:

* Using `for...of` loops, which can be more efficient than traditional `for...in` loops.
* Comparing the performance of using cached arrays versus creating a new array on each iteration.
* Measuring the impact of using SIMD (Single Instruction, Multiple Data) instructions or other parallelization techniques.

Note that these alternatives might require modifying the benchmark code to reflect different scenarios and use cases.

Related benchmarks:

Array loop with cached length (version: 0)

Comparing performance of: With length caching vs Without length caching

Created: 3 years ago by: Registered User

Jump to the latest result

With length caching

Without length caching

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):