Benchmark: internal scope - MeasureThat.net

Script Preparation code:

let x = 0

Tests:

internal scope
let r = 0; for(let i = 0; i < 1000000; i++) { let x = 1; r += x; }
external scope
let r = 0; let x = 0; for(let i = 0; i < 1000000; i++) { x = 1; r += x; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
internal scope
external scope

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:130.0) Gecko/20100101 Firefox/130.0

Browser/OS: Firefox 130 on Linux

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Test name	Executions per second
internal scope	3160.7 Ops/sec
external scope	3324.0 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):

LLMs can make mistakes. Check important info.

This benchmark compares two approaches to variable scoping in JavaScript: **internal scope** and **external scope**. Each test case measures the performance of code that repeatedly assigns a value to a variable (`x`) and accumulates that value into another variable (`r`).

### Test Cases Explained

1. **Internal Scope**:
   ```javascript
   let r = 0;
   for(let i = 0; i < 1000000; i++) {
       let x = 1; // 'x' is declared within the for loop's block scope
       r += x;
   }
   ```
   In this case, the variable `x` is declared inside the loop using the `let` keyword. This creates a new instance of `x` for each iteration of the loop, which means it's scoped to the block of the `for` loop.

2. **External Scope**:
   ```javascript
   let r = 0;
   let x = 0; // 'x' is declared outside the loop
   for(let i = 0; i < 1000000; i++) {
       x = 1; // Reassigning 'x' in each iteration
       r += x;
   }
   ```
   Here, `x` is declared outside of the loop. It is reused across iterations, which might imply that its allocation is more efficient because we're not creating a new variable on each iteration.

### Performance Considerations

- **Internal Scope Pros**:
  - Each iteration has a clean slate with `x`, which can help avoid bugs related to variable state from prior iterations.
  - May be more intuitive for developers who want to ensure that the loop variable does not interfere with other code.

- **Internal Scope Cons**:
  - Higher memory allocation per iteration since a new `x` is created each time, even if the previous one goes out of scope quickly.

- **External Scope Pros**:
  - Potentially less memory overhead because the same `x` variable is reused across iterations. This means less time spent on memory allocation and garbage collection.
  - It can be slightly faster, as evidenced by the benchmark results; `external scope` executed 1565.5 executions per second compared to `1546.5` for `internal scope`.

- **External Scope Cons**:
  - It may lead to harder-to-maintain code if not carefully managed, particularly in complex loops where `x` could be altered unintentionally, and thus might lead to difficult-to-debug errors.

### Benchmark Results Summary

The benchmark results indicate that the external scope implementation performs better in this specific scenario, achieving approximately 1.2% more executions per second compared to the internal scope.

### Alternatives

One alternative to consider is **using `var`** instead of `let`, which would create function-scoped or globally-scoped variables depending on where they are declared. This may result in additional performance impacts based on memory handling differences associated with hoisting and scope.

Another alternative could be to utilize **function scoping** for `x` by encapsulating this logic in a helper function. However, this introduces overhead due to function calls, which may not yield better performance in this context.

In conclusion, while `let` provides clearer scoping rules that can prevent accidental variable collisions, for cases like this where performance is critical, maximizing variable reuse as shown in the external scope can lead to better performance metrics. It’s essential for developers to weigh the benefits of clarity against performance in real-world applications.

Related benchmarks:

internal scope (version: 1)

Comparing performance of: internal scope vs external scope

Created: one year ago by: Guest

Jump to the latest result

internal scope

external scope

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one year ago):