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

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]; }
for of
var sum = 0; for (const ar of arr){ sum = ar; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length
Do not cache
for of

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0

Browser/OS: Firefox 94 on Windows

View result in a separate tab

Test name	Executions per second
Cache length	577454.2 Ops/sec
Do not cache	519696.2 Ops/sec
for of	92208.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and explain what is being tested, the options being compared, their pros and cons, and other considerations.

**Benchmark Definition**

The benchmark measures the performance difference between two approaches:

1. **Caching the array length**: The length of the array is stored in a variable (`var arrLen = arr.length`) before the loop starts. This way, instead of calculating `arr.length` inside the loop, which can be expensive ( especially for large arrays), the value is reused.
2. **Not caching the array length**: The length of the array is not stored in a variable; instead, it's calculated using the `arr.length` expression every time the loop iterates.

**Pros and Cons**

* **Caching the array length**: Pros:
	+ Reduces the number of calculations inside the loop.
	+ Can lead to better performance for loops that iterate over large arrays.
*   Cons:
	+ Requires more memory to store the cached value (`arrLen`).
*   **Not caching the array length**: Pros:
	+ No additional memory is required.
*   Cons:
	+ Calculates `arr.length` every time, which can be expensive.

**For of Loop**

The third test case measures the performance of using a `for...of` loop instead of traditional `for` loops. The `for...of` loop iterates over arrays and objects without requiring an explicit index variable.

Pros:

*   Can lead to better performance for certain use cases, as it eliminates the need for the `length` property access.
*   Can improve readability by avoiding the need to keep track of indices.

Cons:

*   May not be suitable for all types of loops or use cases (e.g., when you need direct index access).
*   Can lead to more complex code if used incorrectly.

**Library: Array.prototype.length**

The `length` property is a built-in property of arrays in JavaScript, which returns the number of elements in the array. This property is used extensively throughout the benchmark to measure performance.

**Special JS feature/Syntax: None mentioned**

No special JavaScript features or syntax are explicitly mentioned in this benchmark definition. However, it's worth noting that some modern browsers may support newer features like `let` and `const` in `for...of` loops, but they don't affect the basic functionality of the loop.

**Other Alternatives**

Alternative approaches to caching array length might include:

*   Using a technique called " memoization" where you cache the result of expensive function calls so that you can reuse it instead of recalculating.
*   Optimizing other parts of the loop, such as reducing unnecessary operations or using more efficient data structures.

However, these alternatives may not be applicable to this specific benchmark, which focuses on measuring performance differences between caching array length and not caching it.

Related benchmarks:

Caching length property vs getting it each time in the loop - ak (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 for of

Created: 3 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

for of

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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