Benchmark: let vs const in tight loops

Tests:

let
let x = 100; let y = x + 1; let z = x + y;
const
const x = 100; const y = x + 1; const z = x + y;

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

let

783.1M/s

const

773.7M/s

View exact numbers

✓ let: 783,051,712 ops/sec
• const: 773,729,472 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
let
const

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 135 on Android

View result in a separate tab

let

75.0M/s

const

68.3M/s

View exact numbers

Test name	Executions per second
✓ let	75,047,360 Ops/sec
const	68,349,120 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the provided benchmark definition and test cases to explain what's being tested, compared, and the pros and cons of different approaches.

**Benchmark Definition**

The benchmark is designed to compare the performance of using `let` versus `const` variables in tight loops. The script preparation code is not provided, but it likely initializes the variables and setup for the loop.

**Test Cases**

There are two test cases:

1. **"let"`**: This test case uses the `let` keyword for variable declarations.
2. **"const"`**: This test case uses the `const` keyword for variable declarations.

**Comparison**

The benchmark is comparing the execution speed of these two approaches in a tight loop. The performance difference between `let` and `const` can be significant, especially when using dynamic typing or changing values.

**Pros and Cons**

* **Let**:
	+ Pros: Dynamic typing allows for more flexibility and ease of use.
	+ Cons: Can lead to slower execution due to reassignment checks during optimization.
* **Const**:
	+ Pros: Enforces immutability, which can improve performance and code reliability.
	+ Cons: Limited flexibility and may require explicit initialization.

**Library Usage**

None of the test cases use any external libraries. The benchmark focuses solely on comparing the performance differences between `let` and `const`.

**Special JS Feature/Syntax**

The benchmark does not explicitly mention or utilize any special JavaScript features or syntax beyond the basic usage of `let` and `const`. However, it's worth noting that modern JavaScript engines often use various optimization techniques that can affect the performance difference between `let` and `const`, such as reassignment checks.

**Other Alternatives**

Some alternative approaches to comparing the performance of `let` and `const` in tight loops include:

1. **Hoisting**: Instead of using `let` or `const`, the benchmark could use hoisted variables (e.g., `var x = 100;`) and measure their execution speed.
2. **Global variables**: The benchmark could compare the performance of global variables (e.g., `x = 100;`) versus local variables (e.g., `let x = 100;`).
3. **Immutable data structures**: The benchmark could use immutable data structures (e.g., arrays or objects with frozen properties) and measure their execution speed.

Keep in mind that each of these alternatives would introduce additional complexity and variations to the benchmark, making it less comparable to the original `let` vs. `const` scenario.

let vs const in tight loops (version: 0)

Checks whether using const helps for performance or not compared to using let everywhere

Comparing performance of: `let vs const`

Created: 2 years ago by: Guest

Go to the latest result

let

const

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

let vs const in tight loops (version: 0)

Checks whether using const helps for performance or not compared to using let everywhere

Comparing performance of: let vs const

Created: 2 years ago by: Guest

Go to the latest result

let

const

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `let vs const`