Benchmark: Caching length property vs getting it each time in the loop

Script Preparation code:

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

Tests:

Cache length
var arrLen = arr.length; var sum = 0; for (var i = 0; i < arrLen; i++){ sum = arr[i]; }
Do not cache
var sum = 0; for (var i = 0; i < arr.length; i++){ sum = arr[i]; }
Reverse
var arrLen = arr.length; var sum = 0; for (var i = arrLen; i !== 0; i--){ sum = arr[i]; }
Reverse Opt
var arrLen = arr.length; var sum = 0; for (; arrLen !== 0; arrLen--){ sum = arr[arrLen]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length
Do not cache
Reverse
Reverse Opt

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 benchmark and explain what's being tested, compared, and the pros and cons of different approaches.

**Benchmark Overview**

The provided JSON represents a JavaScript microbenchmark that compares the performance of three different approaches to access the length property of an array:

1. Caching the length property in a variable (`Cache length`)
2. Not caching the length property (default behavior) (`Do not cache`)
3. Reversing the loop order and accessing elements from the end of the array (`Reverse` and `Reverse Opt`)

**What is being tested?**

The benchmark tests the performance of each approach by iterating over an array of 1000 elements, pushing each element onto the array in a separate iteration. The test measures the execution time per second for each approach.

**Options Compared**

* **Cache length**: Assigns the length property of the array to a variable and uses this value as the loop counter.
	+ Pros: Reduces the number of times the `length` property is accessed, which can improve performance.
	+ Cons: Requires additional memory allocation for the variable, which might not be significant in this case but could impact performance in other scenarios.
* **Do not cache**: Uses the default behavior of accessing the length property directly within the loop.
	+ Pros: No extra memory allocation required.
	+ Cons: Frequent access to the `length` property can lead to additional overhead due to its calculation or caching mechanism.
* **Reverse**: Reverses the order of the loop, starting from the end of the array and accessing elements in reverse order.
	+ Pros: Can be beneficial for certain use cases where the array is sparse or has a specific structure.
	+ Cons: Increases the number of array lookups due to the reversed iteration, which can lead to performance degradation.

**Reverse Opt**

The `Reverse Opt` approach optimizes the reversed loop by using an array index that decrements from the end of the array. This reduces the number of times the array is accessed compared to the standard reverse approach.
	+ Pros: Similar benefits as the standard Reverse approach but with less overhead due to reduced array lookups.
	+ Cons: Requires careful consideration of edge cases and potential corner scenarios.

**Library/ Framework Considerations**

There are no specific libraries or frameworks mentioned in the benchmark definition. However, it's essential to note that the performance differences between these approaches might be influenced by factors like:

* JavaScript engine optimizations
* Array implementation details (e.g., sparse array handling)
* Memory allocation and garbage collection strategies

**Other Alternatives**

Some alternative approaches could be considered for further optimization:

* Using `at` property (ECMAScript 2015+): Accessing elements using the `at` property, which is a more efficient way to access array elements by index.
* Utilizing SIMD instructions: If the JavaScript engine supports SIMD (Single Instruction, Multiple Data) instructions, optimizing the loop for parallel execution could lead to significant performance gains.

Keep in mind that these alternatives might not be relevant or feasible depending on the specific use case and target environment.

Related benchmarks:

Caching length property vs getting it each time in the loop (version: 0)

save length of the array in the variable vs get it the loop

Comparing performance of: Cache length vs Do not cache vs Reverse vs Reverse Opt

Created: 9 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

Reverse

Reverse Opt

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):