Benchmark: Array length variable

Script Preparation code:

array = Array(10000).fill().map(_ => Math.random());

Tests:

With separate length variable
var length = array.length; var sum = 0; for (var i = 0; i < length; ++i) { sum += array[i]; }
Without separate length variable
var sum = 0; for (var i = 0; i < array.length; ++i) { sum += array[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
With separate length variable
Without separate length variable

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
With separate length variable	28705.8 Ops/sec
Without separate length variable	28750.7 Ops/sec

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

LLMs can make mistakes. Check important info.

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

**Benchmark Overview**

The benchmark measures the performance of two different approaches for looping over an array in JavaScript:

1. Using a separate variable to store the length of the array (`var length = array.length;`)
2. Without using a separate variable, instead relying on the `array.length` property directly in the loop condition (`for (var i = 0; i < array.length; ++i) { ... }`)

**Options Compared**

The two options being compared are:

* Option 1: Using a separate variable to store the length of the array. This approach is often referred to as "cached length" or "pre-computed length".
* Option 2: Not using a separate variable, instead relying on `array.length` directly in the loop condition.

**Pros and Cons**

### Option 1 (Cached Length)

Pros:

* Can be faster because the length of the array is only computed once, during script preparation.
* Reduces the number of operations inside the loop.

Cons:

* Requires an additional variable to store the length, which can increase memory usage.
* May not work correctly if the array length changes dynamically (e.g., due to array mutation).

### Option 2 (No Cached Length)

Pros:

* Does not require an extra variable, reducing memory usage.
* Can be more flexible, as it allows for dynamic changes in the loop condition.

Cons:

* Computation of `array.length` is repeated on every iteration, which can lead to slower performance.
* May increase overhead due to the indirect access to `array.length`.

**Other Considerations**

In general, using a separate variable to store the length (Option 1) is recommended when:

* The array size is large and performance is critical.
* The array length is likely to remain constant during the execution of the script.

On the other hand, not using a separate variable (Option 2) might be preferred in situations where:

* Memory usage is a concern, and an extra variable is not acceptable.
* Dynamic changes in the loop condition are expected or necessary.

**Library/External Functionality**

None of the provided benchmark cases uses any external libraries or functions. The script and array creation are performed directly within the benchmark code.

**Special JS Feature/Syntax**

No special JavaScript features or syntax are mentioned in this benchmark case. However, if you'd like to know about other relevant options or alternatives, I can provide some additional context.

**Alternatives**

If you're interested in exploring alternative approaches or optimizations for array looping, here are a few examples:

* Using `for...of` loop instead of traditional `for...in` loop
* Utilizing SIMD instructions (Single Instruction, Multiple Data) for parallel processing
* Leveraging WebAssembly or other just-in-time compilation options

Keep in mind that these alternatives may require additional setup, configuration, and expertise.

Related benchmarks:

Array length variable (version: 0)

Loop over array with/without separate variable for length

Comparing performance of: With separate length variable vs Without separate length variable

Created: 5 years ago by: Guest

Jump to the latest result

With separate length variable

Without separate length variable

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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