Benchmark: var vs let vs const

Tests:

var
var nums = [55, 21, 807, 41, 56, 66, 202]; for(var x = 0; x < nums.length; ++x) { console.log(nums[x]); }
let
let nums = [55, 21, 807, 41, 56, 66, 202]; for(var x = 0; x < nums.length; ++x) { console.log(nums[x]); }
const
const nums = [55, 21, 807, 41, 56, 66, 202]; for(var x = 0; x < nums.length; ++x) { console.log(nums[x]); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
var
let
const

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

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

**What is being tested?**

The test measures the performance difference between three different variable declaration scopes in JavaScript: `var`, `let`, and `const`. The test creates an array of numbers, loops through it, and logs each number to the console using a `for` loop. The goal is to determine which scope provides the best performance.

**Options compared**

The options being compared are:

* `var`: Uses the "variable hoisting" mechanism, where variable declarations are moved to the top of the scope, regardless of their actual declaration position.
* `let`: Uses block scope, where variables are declared within a specific block (e.g., `for`, `if`, `while`) and are not hoisted to the top.
* `const`: Also uses block scope, similar to `let`, but with an additional restriction that variables cannot be reassigned.

**Pros and Cons of each approach**

* `var`:
	+ Pros: None significant
	+ Cons:
		- Variables are "hoisted" to the top of their scope, which can lead to unexpected behavior if not used carefully.
		- Can cause issues with variable naming conflicts due to hoisting.
* `let` and `const`:
	+ Pros:
		- Block scope ensures variables are only accessible within the block they're declared in.
		- No "hoisting" of declarations, reducing potential issues.
	+ Cons:
		- May cause issues if not used carefully, as variable declarations must be within a valid block.
		- Some older browsers or environments may not support `let` and `const`.

**Library usage**

None of the test cases use any external libraries. The benchmark is focused on comparing the performance of different variable declaration scopes.

**Special JS features or syntax**

The test uses some special JavaScript features:

* `for` loops
* Variable declarations (`var`, `let`, `const`)
* Block scope

These features are essential to the structure and logic of the test, which aims to compare the performance differences between these variable declaration mechanisms.

**Alternative approaches**

There are alternative approaches to testing variable declaration performance in JavaScript. Some possible alternatives:

* Test the performance of different loop constructs (e.g., `while`, `do-while`) instead of `for`.
* Compare the performance of variable declaration scopes in different contexts, such as within functions or in object literals.
* Use other microbenchmarking tools or libraries to test specific aspects of JavaScript performance.

Keep in mind that measuring performance differences between small-scale code snippets like this can be challenging and may not accurately reflect real-world usage scenarios. However, it's a useful exercise for understanding the implications of different variable declaration mechanisms on JavaScript performance.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36 Edg/95.0.1020.44

Browser/OS: Chrome 95 on Windows

View result in a separate tab

Test name	Executions per second
var	2481.0 Ops/sec
let	2440.0 Ops/sec
const	2636.6 Ops/sec

Related benchmarks:

var vs let vs const (version: 0)

Comparing performance of: var vs let vs const

Created: 6 years ago by: Guest

Jump to the latest result

var

let

const

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):