Benchmark: const vs let vs var2

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 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/110.0

Browser/OS: Firefox 110 on Linux

View result in a separate tab

Test name	Executions per second
var	15449392.0 Ops/sec
let	15493425.0 Ops/sec
const	14753079.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in this benchmark.

**Overview**

The benchmark compares the performance of three different variable declarations: `var`, `let`, and `const`. The test case uses a simple function `g.o` that pushes an array of numbers onto an object's property `e`.

**Options Compared**

Here are the options being compared:

1. **var**: In older JavaScript versions, `var` declared variables without scoping, which meant they were only accessible within their own block (if any). This led to variable hoisting.
2. **let**: Introduced in ECMAScript 2015 (ES6), `let` declares block-scoped variables, which means they are only accessible within the block where they are declared.
3. **const**: Also introduced in ES6, `const` declares variables that must be constant, meaning their value cannot be changed after declaration.

**Pros and Cons of Each Approach**

1. **var**:
	* Pros: None (performance-wise) since it's outdated and has limitations.
	* Cons:
		+ Variable hoisting can lead to unexpected behavior if not used carefully.
		+ No block scoping, which can make code harder to read and debug.
2. **let**:
	* Pros:
		+ Block scoping makes code more predictable and easier to read.
		+ Avoids variable hoisting issues.
	* Cons: None significant performance-wise, as it's a modern feature with no overhead.
3. **const**:
	* Pros:
		+ Ensures immutability, making code more predictable and maintainable.
		+ Reduces potential bugs due to unexpected variable modifications.
	* Cons:
		+ Can be restrictive if used too liberally (e.g., reassigning a constant variable).
		+ No performance difference compared to `let` in most cases.

**Library and Special JS Feature**

There is no explicit library mentioned, but it's worth noting that the benchmark code uses Array.prototype.push() to push elements onto an array. This is a standard JavaScript method for adding elements to an array.

No special JS features or syntax are used beyond what's inherent to the comparisons (var vs let vs const).

**Other Alternatives**

If you're interested in exploring alternative variable declarations, here are some other options:

1. **let` with block scoping: Introduced in ES6, this declaration provides a more predictable way of declaring variables within blocks.
2. **const` with assignment: Similar to `var`, but ensures the value cannot be changed after initialization.
3. **Destructuring assignments`: Used to extract values from arrays or objects without modifying them.

In summary, this benchmark compares the performance of three variable declarations (var, let, and const) in a simple function that pushes an array onto an object's property. The test results indicate that `let` is slightly faster than `const`, while both are faster than `var`. This helps users understand the performance characteristics of each declaration option in modern JavaScript.

Related benchmarks:

const vs let vs var2 (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):