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]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length
Do not cache
Reverse

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 break down the provided benchmark and explain what is being tested, compared, and its implications.

**Benchmark Overview**

The benchmark compares three approaches to iterate through an array:

1. **Cache length property**: Store the length of the array in a variable (`arrLen`) and use it as the loop condition.
2. **Do not cache**: Simply use the `length` property directly in the loop condition.
3. **Reverse iteration**: Iterate from the end of the array to the beginning using a decrementing counter.

**Comparison**

The benchmark measures the execution time for each approach. The test cases are designed to:

* Test the performance difference between storing and retrieving the length property
* Compare reverse iteration with regular iteration

**Pros and Cons of Each Approach:**

1. **Cache length property**:
	* Pros: Can be faster since it only requires a single lookup.
	* Cons: May lead to incorrect results if the array is modified during iteration (e.g., using `push()`).
2. **Do not cache**:
	* Pros: Simple and straightforward, no risk of modifying the array during iteration.
	* Cons: Requires an additional lookup for the length property, which can be slower.
3. **Reverse iteration**:
	* Pros: Can avoid unnecessary iterations if the array is large and most elements are already at the end.
	* Cons: May require more memory to store the counter variable.

**Library and Special JS Features**

There is no explicit library mentioned in the benchmark, but it uses the `push()` method to append elements to the array. This is a built-in JavaScript method for adding an element to the end of an array.

**Special JS Feature: Iterators**

The benchmark implicitly demonstrates the behavior of iterators in JavaScript arrays. In particular, the use of a decrementing counter (`i--`) in reverse iteration highlights how iterators can be used to iterate through an array in reverse order.

**Other Alternatives**

Some alternative approaches that could be considered for this benchmark include:

* Using `for...of` loops instead of traditional `for...in` loops
* Employing more advanced optimization techniques, such as memoization or caching
* Comparing the performance of different JavaScript engines or virtual machines

Keep in mind that these alternatives might not directly affect the results of this specific benchmark, but they could influence the outcome if used in a different context.

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

Created: 9 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

Reverse

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):