Benchmark: What is the best for the index in the loop let or const ?

Script Preparation code:

var arr = [];

for (let i = 0; i < 1000; i++) {
	arr[i] = i;
}

function someFn(i) {
	return i * 3 * 8;
}

Tests:

let
for (let item of arr) { someFn(item); }
const
for (const item of arr) { someFn(item); }

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: 4 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36

Browser/OS: Chrome 79 on Windows

View result in a separate tab

Test name	Executions per second
let	2752.9 Ops/sec
const	2773.8 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark is designed to compare two approaches: using `let` and using `const` for declaring variables inside a `for...of` loop. The script prepares an array `arr` and then uses a function `someFn` that multiplies its input by 3 and 8.

**Comparison of options**

There are two main options being compared:

1. **`let`**: Declaring the variable with `let` allows it to be reassigned later in the loop.
2. **`const`**: Declaring the variable with `const` makes it immutable, meaning it cannot be reassigned.

**Pros and Cons of each approach**

* **`let`**:
	+ Pros: Reassigning the variable can be useful for updating its value during iteration.
	+ Cons: The variable's value will be updated based on the current loop index `i`, which might lead to unexpected behavior if not carefully planned.
* **`const`**:
	+ Pros: Ensures that the variable's value remains consistent throughout the loop, making it easier to reason about the code.
	+ Cons: Reassigning the variable is not allowed, which can make it harder to update its value during iteration.

**Library**

There is no explicit library being used in this benchmark. However, it's worth noting that `for...of` loops are a part of the ECMAScript standard and do not require any additional libraries.

**Special JS feature or syntax**

The benchmark uses the `for...of` loop syntax, which was introduced in ECMAScript 2015 (ES6). This allows for more concise and readable iteration over arrays and iterables.

**Other alternatives**

There are alternative approaches to iterating over arrays and iterables, such as:

* Using `forEach()`: A function that calls a provided callback function once for each element of an array.
* Using traditional `for` loops with indexing: Accessing elements by their index using `arr[i]`.
* Using `map()`, `filter()`, or other methods that transform arrays without iteration.

It's worth noting that the choice of iteration method often depends on the specific use case and performance requirements.

In this benchmark, the use of `for...of` loops provides a concise and readable way to iterate over the array, while also allowing for easy comparison with other approaches.

Related benchmarks:

What is the best for the index in the loop let or const ? (version: 0)

Comparing performance of: let vs const

Created: 4 years ago by: Guest

Jump to the latest result

let

const

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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