Benchmark: let vs const v5 - MeasureThat.net

Script Preparation code:

const m = new Map([['key', 'value']]);

Tests:

let
let m = new Map([['key', 'value']]); let send = (agg) => {agg.get('key')}; send(m);
const
const m = new Map([['key', 'value']]); const send = (agg) => {agg.get('key')}; send(m);
func
var m = new Map([['key', 'value']]); function send(agg) {agg.get('key')} send(m);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
let
const
func

Fastest: N/A

Slowest: N/A

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net!

**Overview**

The benchmark tests three ways to declare variables in JavaScript: `let`, `const`, and `var`. The goal is to compare the performance of these variables in a specific scenario.

**Test Case Breakdown**

Each test case represents a single variable declaration, with the corresponding function that uses the declared variable. Here's a brief explanation of each test case:

1. **`let m = new Map([['key', 'value']]);`**
	* This is a simple declaration using `let`, which creates a new scope for the variable.
2. **`const m = new Map([['key', 'value']]);`**
	* This uses the `const` keyword, which declares a constant that cannot be reassigned. The variable is still in scope, but it can't be changed.
3. **`var m = new Map([['key', 'value']]);`**
	* This uses the `var` keyword, which creates a global variable by default. The function's scope doesn't affect this variable.

**Library and Syntax Considerations**

The test cases use the `Map` API to store data, but no specific library is required for this benchmark.

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

**Benchmark Results**

The latest results show that:

* **`const m = new Map([['key', 'value']]);`** performs best, with an average of 7282964.5 executions per second.
* **`var m = new Map([['key', 'value']]);`** comes in second, with an average of 8069468.5 executions per second.
* **`let m = new Map([['key', 'value']]);`** has the lowest performance, with an average of 8117547.5 executions per second.

**Pros and Cons**

Here's a brief analysis of each approach:

* **`const m = new Map([['key', 'value']]);`**
	+ Pros: No reassignment issues, clear intention for immutability.
	+ Cons: Can't be changed after declaration.
* **`var m = new Map([['key', 'value']]);`**
	+ Pros: Global scope can be beneficial in some cases.
	+ Cons: Default global scope, potential for naming conflicts.
* **`let m = new Map([['key', 'value']]);`**
	+ Pros: Modern syntax, allows reassignment after declaration.
	+ Cons: May lead to confusion or unexpected behavior if not used carefully.

**Alternatives**

Other alternatives for declaring variables in JavaScript include:

* `let`, which is similar to `const` but can be reassigned.
* `var`, which creates a global variable by default (although it's generally discouraged due to potential naming conflicts and scoping issues).
* Other esoteric or legacy syntax, such as `eval` or ` Function()`, which are not recommended for production code.

In summary, the benchmark results suggest that using `const` for variables is generally the best approach, followed by `var` (though it's still a bit of an older pattern), and then `let`. However, the choice ultimately depends on the specific requirements and constraints of your project.

Latest run results:

Run details: (Test run date: 9 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36

Browser/OS: Chrome 118 on Linux

View result in a separate tab

Test name	Executions per second
let	7282964.5 Ops/sec
const	8117547.5 Ops/sec
func	8069468.5 Ops/sec

Related benchmarks:

let vs const v5 (version: 0)

Comparing performance of: let vs const vs func

Created: 9 months ago by: Guest

Jump to the latest result

let

const

func

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):