Benchmark: cached stop condition in for loop

Script Preparation code:

var totalCount = 0;
var arrayToTest = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]

Tests:

non cached
for(let i = 0; i < arrayToTest.length; i++){ totalCount++; }
cached
let lengthTotal = arrayToTest.length; for(let i = 0; i < lengthTotal; i++){ totalCount++; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
non cached
cached

Fastest: N/A

Slowest: N/A

Latest run results:

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

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I'll break down the provided benchmark and explain what's being tested, compared options, pros/cons, and other considerations.

**Benchmark Overview**

The test cases measure the performance difference between two approaches in a JavaScript loop: one that uses a cached variable (`lengthTotal`) versus one that doesn't use caching (i.e., `arrayToTest.length` is recalculated on each iteration).

**Approach 1: Cached Stop Condition (`let lengthTotal = arrayToTest.length;`)**

In this approach, the `length` property of `arrayToTest` is assigned to a variable `lengthTotal` before the loop starts. This cached value is then used as the condition for the loop.

Pros:

* The loop can exit early if the `length` value changes during execution.
* The compiler may be able to optimize this code better, since it's executed less often.

Cons:

* If the `arrayToTest` array is modified after the loop starts, the cached `lengthTotal` will not reflect these changes, leading to incorrect results or crashes.
* This approach relies on the optimizer to eliminate unnecessary calculations. However, older JavaScript engines might not be able to optimize this as effectively.

**Approach 2: Recalculated Condition (`arrayToTest.length;`)**

In this approach, `length` is recalculated every iteration using `arrayToTest.length`. This means that the loop will always iterate over the entire array, even if its length changes during execution.

Pros:

* More straightforward code, with no risk of crashes due to an outdated or incorrect cached value.
* Can be more reliable for code that needs to account for dynamic changes in the array's size.

Cons:

* The loop may perform unnecessary iterations if the array is modified after it starts executing.
* This approach might lead to slower performance, since the `length` property is recalculated on each iteration.

**Test Results**

The benchmark results show two test cases: "cached" and "non cached." The "cached" test uses Approach 1 with a cached stop condition, while the "non cached" test uses Approach 2 with a recalculated condition. The results are:

| TestName | ExecutionsPerSecond |
| --- | --- |
| cached | 22969.591796875 |
| non cached | 16714.93359375 |

These results suggest that Approach 1 (cached stop condition) performs better, likely due to optimization by the compiler or JavaScript engine.

**Other Considerations**

* Modern JavaScript engines, like V8, have improved their ability to optimize loops with cached conditions.
* If you need to modify the array after starting the loop, using a cached stop condition might be beneficial for performance.
* However, if you're unsure about the modifications or don't want to rely on optimization by the compiler, using a recalculated condition can provide more reliability.

**Alternative Approaches**

Other approaches to consider:

1. **Use `forEach()` instead of `for` loops**: If you need to iterate over an array and perform some operation on each element, consider using `forEach()`, which is designed for this use case.
2. **Leverage `let` or `const` declarations**: Using `let` or `const` declarations can help reduce unnecessary variables and improve performance in certain cases.

Keep in mind that these alternatives might not be directly applicable to this specific benchmark, but they are general best practices in JavaScript development.

Related benchmarks:

cached stop condition in for loop (version: 0)

cached stop condition in for loop

Comparing performance of: non cached vs cached

Created: 6 years ago by: Guest

Jump to the latest result

non cached

cached

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):