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

Script Preparation code:

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

Tests:

Cache length
var sum = 0; for (var i = 0, ii = arr.length; i < ii; i++){ sum = arr[i]; }
Do not cache
var sum = 0; for (var i = 0; i < arr.length; 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

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):

LLMs can make mistakes. Check important info.

Let's dive into the provided benchmark definition and test cases.

**Benchmark Definition**

The benchmark measures the performance difference between two approaches: caching the length of an array versus retrieving it each time within a loop. The script preparation code initializes an empty array `arr` with 1000 elements, and then uses a for loop to push elements into the array.

There are two variations:

1. **Cache length**: In this approach, the length of the array is stored in a variable `ii` and used as the condition in the loop.
2. **Do not cache**: In this approach, the length of the array is accessed within the loop using `arr.length`.

**Options Compared**

The two options being compared are:

1. Caching the length of the array (`var ii = arr.length;`) to reduce the number of iterations.
2. Not caching the length of the array (`i < arr.length;`) and retrieving it each time within the loop.

**Pros and Cons**

**Caching the length:**

Pros:

* Reduces the number of array lookups, which can be expensive operations in JavaScript.
* Can lead to better performance, especially for large arrays.

Cons:

* Requires storing the length of the array in a variable (`ii`), which may add some memory overhead.
* May not be suitable for arrays that are constantly changing size or have unpredictable lengths.

**Not caching the length:**

Pros:

* Does not require storing any additional variables or memory.
* Can be simpler to implement and understand.

Cons:

* Leads to more array lookups, which can be slower than caching the length.
* May result in worse performance for large arrays.

**Other Considerations**

In general, caching the length of an array can lead to better performance, especially when dealing with large datasets. However, it's essential to consider the memory overhead and potential impact on other variables or scope.

Additionally, if the array is constantly changing size or has unpredictable lengths, caching the length might not be suitable. In such cases, not caching the length and retrieving it each time within the loop may be a better choice.

**Library and Purpose**

In this benchmark, no specific library is used. The test script only uses basic JavaScript features and syntax.

**Special JS Feature or Syntax**

There are no special JS features or syntax mentioned in the benchmark definition.

**Alternative Approaches**

Other alternatives to caching the length of an array could include:

* Using a more efficient data structure, such as a sparse array or a linked list.
* Employing lazy evaluation or memoization techniques to reduce the number of array lookups.
* Optimizing the loop itself using techniques like unrolling or parallelization.

However, these alternatives may require additional setup and tuning to achieve optimal performance.

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.135 Safari/537.36

Browser/OS: Chrome 84 on Windows

View result in a separate tab

Test name	Executions per second
Cache length	11879.4 Ops/sec
Do not cache	5900.4 Ops/sec

Related benchmarks:

Caching length property vs getting it each time in the 'for' 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

Created: 4 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 25 days ago):