Benchmark: Array.length in loop VS Array.length out of loop

Script Preparation code:

var a = []

Tests:

Array.length in loop
for(let i = 0; i < a.length; i++){ console.log('test case 1: ', i) }
Array.length out of loop
const size = a.length for(let i = 0; i < size; i++){ console.log('test case 2: ', i) }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Array.length in loop
Array.length out of loop

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36

Browser/OS: Chrome 125 on Windows

View result in a separate tab

Test name	Executions per second
Array.length in loop	6968550.0 Ops/sec
Array.length out of loop	7421838.5 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 definition and test cases.

**Benchmark Definition**

The provided JSON represents a JavaScript microbenchmarking framework called MeasureThat.net. The benchmark is designed to measure the performance of two approaches for accessing the length property of an array in a loop:

1.  **Array.length in loop**: This approach uses the `a.length` expression inside a loop to access the array's length.
2.  **Array.length out of loop**: This approach assigns the result of `a.length` to a variable `size` and then uses this variable inside the loop to access the array's length.

**Options Compared**

The benchmark compares the performance of these two approaches:

*   Pros of Array.length in loop:
    *   Simplified code: The code is more straightforward, as it doesn't require an additional assignment.
    *   Less memory allocation: Since `a.length` is not assigned to a new variable, there's less memory allocation overhead.
*   Cons of Array.length in loop:
    *   Potential for array resizing: If the array grows or shrinks during execution, `a.length` will become outdated, leading to incorrect results.
*   Pros of Array.length out of loop:
    *   More accurate results: The `size` variable ensures that the correct number of iterations is performed, even if the array size changes.
    *   Better handling of array resizing: Since `size` is updated only when necessary, this approach can handle array resizing more effectively.

**Pros and Cons**

The choice between these approaches depends on the specific requirements and constraints of your project. If accuracy and robustness are crucial, using `Array.length out of loop` might be a better option. However, if simplicity and performance are priorities, `Array.length in loop` could be sufficient.

**Library Used (None)**

There is no library used in this benchmark definition.

**Special JavaScript Feature or Syntax**

The benchmark uses the following special features:

*   **Template literals**: The `Benchmark Definition` JSON uses template literals to format the string values.
*   **Arrow functions**: Some test cases use arrow functions (`=>`) for simplicity and conciseness.

**Other Alternatives**

If you need alternative approaches, here are some options:

1.  **Using `Array.prototype.length` instead of bracket notation**: You can access an array's length using the `length` property on the `Array.prototype`, like this: `[].length`. However, this approach is similar to `Array.length in loop`.
2.  **Using a separate variable for the array size**: Similar to `Array.length out of loop`, you can assign the array size to a new variable outside the loop and then use that variable inside the loop.
3.  **Using JavaScript's `at()` method**: If you're using modern browsers, you can use the `at()` method to access an element in an array without having to specify its index.

Keep in mind that these alternatives might not provide a significant performance improvement over the original approaches and should be used based on your specific requirements and constraints.

Related benchmarks:

Array.length in loop VS Array.length out of loop (version: 0)

Comparing performance of: Array.length in loop vs Array.length out of loop

Created: one year ago by: Guest

Jump to the latest result

Array.length in loop

Array.length out of loop

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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