Benchmark: const vs let vs var fixed

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 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0

Browser/OS: Firefox 115 on Windows

View result in a separate tab

Test name	Executions per second
var	13131040.0 Ops/sec
let	12681305.0 Ops/sec
const	12763114.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks.

**What is being tested?**

The provided JSON represents a benchmark that tests the performance difference between three variable declarations: `const`, `let`, and `var`. Each test case uses the same script, but with different variable declarations.

**Options compared**

The benchmark compares the performance of these three options:

* `var`: The traditional way of declaring variables in JavaScript. Variables declared with `var` are function-scoped, which means they can be accessed from anywhere within a function.
* `let`: Introduced in ECMAScript 2015 (ES6), `let` is a block-scoped variable declaration. This means that variables declared with `let` can only be accessed within the scope of the block or statement where it's declared.
* `const`: Also introduced in ES6, `const` is used to declare immutable variables. Like `let`, variables declared with `const` are block-scoped.

**Pros and Cons**

* **Var**:
	+ Pros: Has been the standard for a long time, widely supported by browsers and environments.
	+ Cons: Can lead to unexpected behavior due to its function-scoping nature, making it harder to reason about code.
* **Let**:
	+ Pros: Improves code readability by clearly indicating block scope, reduces potential for variable pollution.
	+ Cons: May require more explicit variable declarations, can be less familiar to developers without ES6 experience.
* **Const**:
	+ Pros: Makes the intent of a variable clear, reduces bugs due to unintentional mutation.
	+ Cons: May seem restrictive or unnecessary for simple variables.

**Library usage**

There is no library mentioned in the provided benchmark definition. The script and HTML preparation codes are empty, suggesting that this benchmark focuses solely on the performance characteristics of `var`, `let`, and `const` declarations.

**Special JavaScript features/syntax**

The benchmark uses the `function` keyword to declare a function `o` with two parameters, `x`. No special syntax or features are used here.

**Other alternatives**

If you're interested in exploring more alternatives or variants of variable declarations, consider looking into:

* `let const`: This is an experimental feature in some browsers and environments that combines the benefits of both `let` and `const`.
* Dynamic variables (e.g., using `var foo = bar;`). These can lead to performance issues due to hoisting.
* Hoisted variables (e.g., declaring a variable without initialization). This behavior can be surprising for developers.

When working with JavaScript, it's essential to consider the trade-offs between different approaches and understand how they impact code readability, maintainability, and performance. The provided benchmark helps demonstrate the benefits of using `let` and `const` declarations in modern JavaScript development.

Related benchmarks:

const vs let vs var fixed (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 2 months ago):