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; 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:

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in the provided benchmark.

**General Overview**

The test compares different approaches to accessing the length of an array within a loop:

1. **Cache length**: Store the length of the array in a variable and use it instead of recalculating it on each iteration.
2. **Do not cache**: Recalculate the length of the array on each iteration.

**Reverse**

In addition to these two approaches, there are also two variations that differ in how the loop is structured:

1. **Reverse**: The loop starts from the last element of the array and iterates backwards using `arrLen` as the starting point.
2. **Reverse Opt**: This variation uses a base variable (`base`) that increments from 0 to `arrLen - 1`, which is more efficient than iterating from `arrLen` to 0.

**Library and Special JS Features**

There are no libraries explicitly mentioned in the benchmark definition or test cases.

However, it's worth noting that JavaScript has some special features related to array iteration, such as:

* **For...of loop**: Introduced in ECMAScript 2015 (ES6), this loop iterates over an array using a "for...of" syntax. While not used in the benchmark, it's another way to iterate over arrays.
* **Array.prototype.forEach() and friends**: These methods provide more convenient ways to iterate over arrays, but are not relevant to this specific benchmark.

**Pros and Cons of Each Approach**

Here's a brief summary:

1. **Cache length**:
	* Pros: Faster execution times since the length is only calculated once.
	* Cons: Requires an extra variable to store the length, which may impact memory usage.
2. **Do not cache**:
	* Pros: No additional variables needed, making it more concise and potentially easier to read.
	* Cons: Recalculating the length on each iteration can lead to slower execution times.

The **Reverse** and **Reverse Opt** variations differ mainly in their loop structure:

1. **Reverse**:
	* Pros: May be slightly faster due to the reduced number of iterations required.
	* Cons: Less intuitive for some developers, as it starts from a fixed index rather than 0.
2. **Reverse Opt**:
	* Pros: More efficient since it uses a base variable that increments more quickly.
	* Cons: Requires careful consideration of edge cases and potential overflow issues.

**Other Alternatives**

Other ways to improve performance in this benchmark might include:

1. Using **Array.prototype.forEach()**: While not directly relevant, using `forEach()` could simplify the code and potentially lead to better performance due to optimized iteration logic.
2. Minimizing array access overhead: Reducing the number of array accesses per iteration (e.g., by reusing elements or using iterators) might improve performance.

Keep in mind that these alternatives are not directly related to the specific question asked, which is primarily focused on comparing different approaches to accessing an array length.

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):