Benchmark: const vs let vs var 42

Tests:

var
var g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
let
let g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
const
const g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()

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

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/115.0

Browser/OS: Firefox 115 on Mac OS X 10.15

View result in a separate tab

Test name	Executions per second
var	23389598.0 Ops/sec
let	21867036.0 Ops/sec
const	23367638.0 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 provided benchmark and explain what is being tested, compared, and other considerations.

**What is being tested?**

The benchmark compares the performance of three variables in JavaScript: `var`, `let`, and `const`. Each variable is used to declare a variable `g` with an empty array `e`, and then defines a function `o` that pushes elements into the array. The function `o` is called multiple times.

**Options compared**

The benchmark compares three options:

1. `var g = { e: [] }`
2. `let g = { e: [] }`
3. `const g = { e: [] }`

**Pros and Cons of each approach**

* `var`:
	+ Pros: None
	+ Cons:
		- Variables are "hoisted" to the top of their scope, which can lead to unexpected behavior.
		- The variable is not "block-scoped", meaning it's not isolated to a specific block of code.
* `let`:
	+ Pros:
		- Variables are "declared with let" and are only scoped to the block they're inside.
		- Reduces polluting the global scope.
	+ Cons: None significant in this case
* `const`:
	+ Pros:
		- Variables are immutable by default, which can prevent unintended changes.
		- Reduces polluting the global scope.
	+ Cons:
		- Variables cannot be reassigned after they're declared.

**Library and purpose**

In none of the provided benchmark definitions, there is a library mentioned. However, some JavaScript engines (like V8 in Chrome) have built-in optimizations and features that can affect the performance of variable declarations.

**Special JS feature or syntax**

There are no special JS features or syntax used in this benchmark, apart from `const` which was introduced later than `let`. The only thing being tested is the difference between these three variable declarations.

**Other alternatives**

If you were to compare the performance of different types of variables (e.g., `let`, `const`, and `var`) on their own without declaring a function, it might be interesting to also include:

* `var` with `let` or `const` declared inside
* `let` with `const` declared inside
* `const` with another constant value

However, in this specific benchmark, the performance difference is likely due to the differences between variable declarations and function execution.

It's worth noting that modern JavaScript engines have various optimizations and caching mechanisms that can affect the performance of these benchmarks. The actual performance results may vary depending on the JavaScript engine, browser, and other factors.

Related benchmarks:

const vs let vs var 42 (version: 0)

Comparing performance of: var vs let vs const

Created: one year 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 one month ago):