Benchmark: Compare the cost of Array.prototype.length

Script Preparation code:

var array = [];
for(var i = 0; i < 1000; i++){
  array[i] = i;
}

Tests:

Using Array.prototype length all the time
var sum = 0; for (var i = 0; i < array.length; i++) { sum += array[i]; }
Caching the value of Array.prototype.length
var sum = 0; var len = array.length; for (var i = 0; i < len; i++) { sum += array[i]; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Using Array.prototype length all the time
Caching the value of Array.prototype.length

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 29 days ago):

LLMs can make mistakes. Check important info.

Let's dive into explaining what's being tested in this benchmark.

The benchmark is comparing two approaches to accessing the length of an array: using `Array.prototype.length` directly and caching its value in a variable. The test cases are designed to measure the performance difference between these two methods.

**Approach 1: Using `Array.prototype.length` all the time**

In this approach, the code uses `array.length` directly inside the loop. This means that for every iteration of the loop, the length of the array is accessed again and again.

Pros:

* Easy to read and maintain
* No additional memory allocation or variable storage needed

Cons:

* Potential performance overhead due to repeated accesses to `array.length`

**Approach 2: Caching the value of `Array.prototype.length`**

In this approach, the code stores the length of the array in a variable `len` before the loop. Then, it uses `len` instead of `array.length` inside the loop.

Pros:

* Reduced number of accesses to `array.length`, which can improve performance
* Potentially faster loop execution

Cons:

* Additional memory allocation and storage for the `len` variable
* More complex code to manage the variable

**Library: None**

There are no libraries used in this benchmark. The test cases only utilize built-in JavaScript features.

**Special JS feature or syntax: None**

There are no special JavaScript features or syntax being tested in this benchmark.

Now, let's discuss other alternatives:

1. **Using `Array.prototype.length` with a cache**: A variation of Approach 2, where the length is cached once and reused for multiple iterations.
2. **Using an iterator**: Instead of using `array.length`, the code could use an iterator to access each element in the array without having to keep track of the length.
3. **Pre-compiling the loop**: Some engines (like V8) allow pre-compilation of loops, which can eliminate the need for repeated accesses to `array.length`.

In summary, this benchmark tests the performance difference between two approaches to accessing the length of an array: using `Array.prototype.length` directly and caching its value in a variable.

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.60 Safari/537.36

Browser/OS: Chrome 100 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
Using Array.prototype length all the time	9231.5 Ops/sec
Caching the value of Array.prototype.length	18509.3 Ops/sec

Related benchmarks:

Compare the cost of Array.prototype.length (version: 0)

This benchmark is to compare if storing the length of an array in a variable is valuable when it is needed to access this data multiple times

Comparing performance of: Using Array.prototype length all the time vs Caching the value of Array.prototype.length

Created: 5 years ago by: Registered User

Jump to the latest result

Using Array.prototype length all the time

Caching the value of Array.prototype.length

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 29 days ago):