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

Script Preparation code:

var arr = [];
var count = 25000;
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; var base = 0; for (; base !== arrLen; base++){ sum = arr[base]; }

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:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:136.0) Gecko/20100101 Firefox/136.0

Browser/OS: Firefox 136 on Windows

View result in a separate tab

Test name	Executions per second
Cache length	22095.3 Ops/sec
Do not cache	22463.9 Ops/sec
Reverse	18907.2 Ops/sec
Reverse Opt	18871.8 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explain what's being tested.

**Benchmark Overview**

The benchmark measures the performance of different approaches to accessing an array's length property versus performing calculations within a loop.

**Options Compared**

There are four test cases:

1. **Cache length**: The array's length is cached in a variable `arrLen` before the loop, and then used as the loop condition.
2. **Do not cache**: The array's length is not cached, and instead, the `length` property is accessed within the loop on each iteration.
3. **Reverse**: The loop iterates over the array from the end to the beginning (i.e., `arr.length - 1`, `arr.length - 2`, ...), rather than from start to finish.
4. **Reverse Opt**: A variation of the "Reverse" approach, where the loop iterates over the array in reverse order, but using a different optimization technique.

**Pros and Cons of Each Approach**

* **Cache length**:
	+ Pros: Reduces the number of times `length` is accessed within the loop, which can improve performance.
	+ Cons: Requires an additional variable to cache the result, which may increase memory usage.
* **Do not cache**: No additional variables are used, and the loop only accesses `length` on each iteration. This approach has higher overhead due to repeated accesses to `length`.
* **Reverse**:
	+ Pros: Can be faster for arrays with a large number of elements since it avoids the need to iterate over the entire array.
	+ Cons: Requires an additional loop counter variable, which can increase memory usage and may not be necessary if only accessing `length` is needed.
* **Reverse Opt**: This approach combines the benefits of both "Reverse" and "Cache length". By iterating in reverse order, it avoids the need to access `length` repeatedly, while still caching the result once.

**Library and Special JS Features**

There are no libraries mentioned in the benchmark JSON. However, some JavaScript features may be used implicitly, such as:

* **Loops**: For loops (`for`) are used throughout the benchmarks.
* **Variables**: Variables (e.g., `arr`, `i`, `sum`) are declared and reused.

**Other Considerations**

The benchmark measures the performance of different approaches to accessing an array's length property. The results will show which approach is faster for this specific use case.

**Alternatives**

If you're looking for alternative methods or variations, consider:

* **Using `Array.prototype.forEach()`**: Instead of using traditional loops, consider using the `forEach()` method, which can provide better performance and readability.
* **Caching intermediate results**: If there are other calculations that need to be performed within the loop, consider caching intermediate results to avoid repeated accesses.
* **Profile-guided optimization**: Use profiling tools to identify performance bottlenecks in your code and optimize those specific areas.

Keep in mind that the choice of approach depends on the specific use case and requirements. The benchmark JSON provides a good starting point for exploring different optimization strategies.

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

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):