Benchmark: Caching length property (internal and external) 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 (external)
var arrLen = arr.length; var sum = 0; for (var i = 0; i < arrLen; i++){ sum = arr[i]; }
No cache
var sum = 0; for (var i = 0; i < arr.length; i++){ sum = arr[i]; }
Cache length (internal)
var sum = 0; for (var i = 0, arrLen = arr.length; i < arrLen; i++){ sum = arr[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length (external)
No cache
Cache length (internal)

Fastest: N/A

Slowest: N/A

Latest run results:

No previous 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 its test cases to explain what's being tested, compared, and their pros and cons.

**Benchmark Overview**

The benchmark tests three approaches to accessing the length of an array in a loop:

1. Caching the length externally (using `arr.length`)
2. Not caching the length at all (only using `arr.length` within the loop)
3. Caching the length internally (using `arr.length` outside the loop)

**Test Cases**

### 1. Cache length (external)

```javascript
var arrLen = arr.length;
for (var i = 0; i < arrLen; i++) {
  sum = arr[i];
}
```

This approach caches the length of the array in a separate variable (`arrLen`) before the loop, reducing the need to access `arr.length` multiple times within the loop.

Pros:

* Reduces cache misses and accesses, potentially improving performance.
* Can be beneficial for large arrays where accessing `arr.length` is expensive.

Cons:

* Requires an additional variable to store the cached length.
* May not be suitable for all use cases, as it introduces extra memory usage.

### 2. No cache

```javascript
for (var i = 0; i < arr.length; i++) {
  sum = arr[i];
}
```

This approach does not cache the length of the array at all, relying solely on accessing `arr.length` within the loop.

Pros:

* Simplifies code and eliminates the need for an additional variable.
* Suitable for small arrays or performance-critical loops where every cycle counts.

Cons:

* May result in more cache misses and accesses, potentially decreasing performance.
* Can be slower for large arrays due to increased cache thrashing.

### 3. Cache length (internal)

```javascript
var sum = 0;
for (var i = 0, arrLen = arr.length; i < arrLen; i++) {
  sum = arr[i];
}
```

This approach caches the length of the array internally using `arr.length` outside the loop and only once.

Pros:

* Balances between caching and simplicity.
* Suitable for most use cases where accessing `arr.length` within the loop is relatively cheap.

Cons:

* May not be as efficient as external caching (see above) but still offers some benefits.
* Can introduce extra memory usage due to the additional variable.

**Library Usage**

None of the test cases explicitly use any JavaScript libraries, frameworks, or modules.

**Special JS Features/Syntax**

No special JavaScript features or syntax are used in these benchmark test cases. They focus solely on basic array iteration and caching mechanics.

**Alternatives**

Other alternatives for this benchmark could include:

* Using `Array.prototype.forEach()` or other built-in array methods that optimize cache usage.
* Implementing a custom caching mechanism using techniques like memoization or caching libraries.
* Comparing different array data structures, such as using linked lists instead of arrays.
* Investigating how various browser optimizations, like Just-In-Time (JIT) compilation or ahead-of-time (AOT) compilation, affect performance.

These alternatives would require additional modifications to the benchmark and test cases to accommodate new techniques and assumptions about the target environment.

Related benchmarks:

Caching length property (internal and external) 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 (external) vs No cache vs Cache length (internal)

Created: 3 years ago by: Guest

Jump to the latest result

Cache length (external)

No cache

Cache length (internal)

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):