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 llama3.1:latest, generated one year ago):

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**Benchmark Definition**

The provided JSON represents a benchmark definition named "Variable declaration inside or outside for loop (less data 2)". This benchmark measures the performance difference between declaring variables inside and outside a `for` loop. The script preparation code generates an array `data` with 1000 objects, each containing a random integer value.

**Test Cases**

There are two individual test cases:

1. **"declaration inside for loop"**: In this case, three arrays (`array1`, `array2`, and `array3`) are declared inside the `for` loop. Each iteration creates new arrays using array methods (`filter`, `map`, and `push`). The data is filtered to include only values greater than 50, mapped to add 1 to each value, and then pushed onto the respective arrays.
2. **"declaration outside for loop"**: In this case, three arrays (`array1`, `array2`, and `array3`) are declared outside the `for` loop. The same array methods are used inside the loop to update these pre-existing arrays.

**Library and Special JS Features**

No external libraries or special JavaScript features are used in these test cases.

**Pros and Cons of Approaches**

The benchmark measures the performance difference between declaring variables inside and outside a `for` loop. This can help developers understand how variable declaration affects code execution speed.

* **Pros of declaring inside for loop**: Variables are only in scope within the loop, reducing memory usage and potential garbage collection overhead.
* **Cons of declaring inside for loop**: Each iteration creates new variables, which might lead to increased execution time due to function calls (e.g., `filter`, `map`).
* **Pros of declaring outside for loop**: Pre-existing variables can be reused within the loop, reducing the number of function calls and potential overhead.
* **Cons of declaring outside for loop**: Variables remain in scope after the loop finishes, potentially increasing memory usage.

**Other Considerations**

The benchmark results show that declaring variables inside the `for` loop yields a slightly lower execution speed (3.404924154281616 vs 3.3670034408569336 executions per second) compared to declaring them outside the loop on Chrome 102 browser.

**Alternatives and Recommendations**

To optimize variable declaration:

* Declare variables only when necessary, using a scope that matches their usage.
* Reuse pre-existing variables within loops, if possible.
* Consider using `const` for variables that don't change value after initialization.
* If you need to declare multiple variables inside a loop, consider grouping them in an object or array to reduce scope and potential overhead.

Keep in mind that the performance difference may vary depending on your specific use case, browser version, and system configuration. Always profile your code with real-world data to make informed optimization decisions.

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 llama3.1:latest, generated one year ago):