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 = 0; i === 0; i--){ sum = arr[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Cache length
Do not cache
Reverse

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

**Benchmark Definition**

The benchmark tests three different approaches to iterating over an array in JavaScript:

1. **Cache length property**: This approach saves the length of the array in a variable (`arrLen`) and uses it as the condition for the loop.
2. **Do not cache**: This approach does not save the length of the array and relies on the `length` property of the array being calculated each time the loop iterates.
3. **Reverse**: This approach has an unusual logic, where the loop counter (`i`) is set to 0 initially and decremented in each iteration.

**Options Compared**

The benchmark compares the performance of these three approaches:

* Cache length property: saves the array length in a variable and uses it as the condition for the loop.
* Do not cache: calculates the array length on each iteration of the loop.
* Reverse: has an unusual logic, where the loop counter is decremented instead of incremented.

**Pros and Cons**

1. **Cache length property**:
	* Pros: can be faster if the array length is small or constant.
	* Cons: requires saving the array length in a variable, which may consume additional memory.
2. **Do not cache**:
	* Pros: does not require extra memory allocation.
	* Cons: can be slower due to repeated calculations of the array length.
3. **Reverse**:
	* Pros: None apparent.
	* Cons: has an unusual logic that might make it harder to understand and maintain.

**Library Usage**

There is no explicit library usage in this benchmark definition.

**Special JS Feature/Syntax**

None mentioned.

Now, let's discuss other alternatives:

1. **Using a for...of loop**: This approach would eliminate the need to calculate the array length on each iteration.
2. **Using Array.prototype.slice() or Array.prototype.subarray()**: These methods can be used to create a new array with the desired length, eliminating the need to calculate the original array's length.

In summary, the benchmark tests three different approaches to iterating over an array in JavaScript and compares their performance. Understanding the pros and cons of each approach is essential to determine which one is best suited for a particular use case.

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

Created: 9 years ago by: Guest

Jump to the latest result

Cache length

Do not cache

Reverse

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):