Benchmark: Variable declaration inside or outside for loop (less data 2)

Script Preparation code:

function getRandomInt(max) {
  return Math.floor(Math.random() * Math.floor(max));
}

var data = [];
for(var i = 0; i < 1000; i++){
  data.push({value:getRandomInt(100)});
}

Tests:

declaration inside for loop
for (let i = 0; i < 1000; i++) { let array1 = []; let array2 = []; let array3 = []; array1.push(... data.filter(n => n > 50).map(n => n + 1)); array2.push(... data.filter(n => n > 50).map(n => n + 1)); array3.push(... data.filter(n => n > 50).map(n => n + 1)); }
declaration outside for loop
let array1 = []; let array2 = []; let array3 = []; for (let i = 0; i < 1000; i++) { array1 = []; array2 = []; array3 = []; array1.push(... data.filter(n => n > 50).map(n => n + 1)); array2.push(... data.filter(n => n > 50).map(n => n + 1)); array3.push(... data.filter(n => n > 50).map(n => n + 1)); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
declaration inside for loop
declaration outside for loop

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model gemma2:9b, generated one year ago):

LLMs can make mistakes. Check important info.

This benchmark tests the performance difference between declaring arrays inside and outside of a `for` loop in JavaScript.

Here's a breakdown:

**Options Compared:**

* **"declaration inside for loop":** Arrays (`array1`, `array2`, `array3`) are declared within each iteration of the `for` loop.
* **"declaration outside for loop":** Arrays (`array1`, `array2`, `array3`) are declared *before* the `for` loop, and new arrays are created in each iteration.

**Pros/Cons:**

* **Inside the Loop:** 
    * **Potentially Faster (in some cases):**  Memory allocation for the arrays happens within the loop, which might reduce initial overhead. However, this also means more frequent memory allocations.
    * **Can be Less Readable:**  Multiple declarations within a loop can make the code harder to follow.

* **Outside the Loop:** 
    * **More Readable:** The code structure is simpler and easier to understand.
    * **Potentially Slower (in some cases):**  The initial allocation of arrays outside the loop might take longer, but memory reallocation happens less frequently.

**Other Considerations:**

* **Garbage Collection:** JavaScript's garbage collector can significantly impact performance depending on how it manages memory allocations and deallocations. The frequency of array creation and destruction in each scenario could influence garbage collection behavior.
* **Compiler Optimizations:** Modern JavaScript engines often optimize code extensively, so the performance difference between these approaches might be very subtle or non-existent in practice.

**Alternatives:**

* **Array Methods:** Consider using efficient array methods like `filter` and `map` instead of manually creating new arrays within the loop. These methods are typically optimized by the JavaScript engine.

Let me know if you have any other questions!

Related benchmarks:

Variable declaration inside or outside for loop (less data 2) (version: 0)

Comparing performance of: declaration inside for loop vs declaration outside for loop

Created: 6 years ago by: Guest

Jump to the latest result

declaration inside for loop

declaration outside for loop

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model gemma2:9b, generated one year ago):