Benchmark: grthyvar vs let vs constndj

HTML Preparation code:

<!--your preparation HTML code goes here-->

Script Preparation code:

let arr = Array(3e6).fill(()=>{})

Tests:

var
for(var o of arr) o()
let
for(let o of arr) o()
const
for(const o of arr) o()
outside - var
var o for(o of arr) o()
outside - let
let o for(o of arr) o()
global
for(o of arr) o()

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
var
let
const
outside - var
outside - let
global

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 133 on Android

View result in a separate tab

Test name	Executions per second
var	14.0 Ops/sec
let	14.0 Ops/sec
const	14.0 Ops/sec
outside - var	14.1 Ops/sec
outside - let	14.0 Ops/sec
global	1.2 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 2 months ago):

LLMs can make mistakes. Check important info.

The benchmark test represented in the provided JSON focuses on comparing the performance of different variable declaration options in JavaScript, specifically `var`, `let`, and `const`. It also examines the impact of using these declarations in various scopes, including the global scope and the use of an outer-scope variable in a for-of loop.

### Options Compared:

1. **`for (var o of arr) o()`**:
   - **Test Name:** `var`
   - Uses the `var` declaration, which has function scope.
   
2. **`for (let o of arr) o()`**:
   - **Test Name:** `let`
   - Uses the `let` declaration, which has block scope.

3. **`for (const o of arr) o()`**:
   - **Test Name:** `const`
   - Uses the `const` declaration, which is also block-scoped, but indicates that the variable `o` cannot be reassigned.

4. **`var o; for (o of arr) o()`**:
   - **Test Name:** `outside - var`
   - Declares the variable `o` outside the loop using `var`. The scope of `o` is still global or function scope.

5. **`let o; for (o of arr) o()`**:
   - **Test Name:** `outside - let`
   - Similar to above but using `let`, giving it block scope when within a block (not function).

6. **`for (o of arr) o()`**:
   - **Test Name:** `global`
   - Directly uses the variable `o` without declaration. This generally pulls `o` from the global context.

### Benchmark Results:

The performance outcomes (in terms of executions per second) of these tests indicate some trends:

- **`outside - var`:** Highest performance with approximately 14.06 executions per second.
- **`outside - let`:** A close second at approximately 14.03 executions per second, noting that using `let` in an outer context still provides significant performance.
- **`let`:** Slightly lower performance at approximately 14.01 executions per second, possibly due to scope-related overhead.
- **`var`:** Similar performance at approximately 13.99 executions per second.
- **`const`:** Lowest performance among the block-scoped options at approximately 13.98 executions per second.
- **`global`:** Significantly lower performance at approximately 1.15 executions per second, indicating the overhead of looking up the variable directly in the global scope.

### Pros and Cons of Approaches:

- **`var`:**
  - **Pros:** High performance; familiar to many developers.
  - **Cons:** Functionally scoped, can lead to unexpected behaviors, especially in nested functions.

- **`let`:**
  - **Pros:** Block-scoped, leading to fewer unintended side effects; well-suited for block iterations.
  - **Cons:** Slightly more overhead compared to `var`, but often negligible in most cases.

- **`const`:**
  - **Pros:** Ensures immutability of variable reference, which can prevent unintentional changes.
  - **Cons:** May have slightly lower performance due to its immutable nature.

- **Global Scope:**
  - **Pros:** Quick accessibility.
  - **Cons:** High potential for name collisions and performance penalty leading to slower execution times.

### Other Considerations:

1. **Closure Behavior:** All declarations (`var`, `let`, and `const`) have implications on closures within loops which affect performance, especially if used in large datasets or complex iterations.
   
2. **Memory Management:** While `var` and `let` may behave similarly in destructive contexts, `const` ensures that bindings remain unchanged and may be better for memory optimization.

3. **Best Practices:** ES6 introduced `let` and `const` to improve code clarity and reduce errors. In modern JavaScript development, `let` and `const` are recommended over `var` due to their scope control.

### Alternatives:

- **Function Scope Alternative:** Declaring variables inside function parameters or inside blocks can also be used instead of using global variables.
  
- **Using Higher-Order Functions:** Instead of traditional looping constructs, using methods like `.map()`, `.forEach()`, and `.reduce()` can lead to more readable code and sometimes improved browser optimizations.

- **Performance Libraries:** For critical performance components, libraries like `lodash` can be utilized to provide optimized functions, albeit at the cost of additional dependencies.

In summary, this benchmark sheds light on the subtle performance differences and proper usage contexts of `var`, `let`, `const`, and highlights modern best practices in JavaScript variable declaration.

Related benchmarks:

grthyvar vs let vs constndj (version: 1)

Comparing performance of: var vs let vs const vs outside - var vs outside - let vs global

Created: 2 months ago by: Guest

Jump to the latest result

var

let

const

outside - var

outside - let

global

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 2 months ago):