Benchmark: var vs let vs const

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 (iPhone; CPU iPhone OS 16_3_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.3 Mobile/15E148 Safari/604.1

Browser/OS: Mobile Safari 16 on iOS 16.3.1

View result in a separate tab

Test name	Executions per second
var	23236454.0 Ops/sec
let	21377570.0 Ops/sec
const	20116366.0 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 benchmark test cases.

**What is being tested?**

The provided JSON represents a benchmarking test case that compares the performance of three variable declarations in JavaScript: `var`, `let`, and `const`. Each test case creates an object `g` with an empty array `e` and defines a function `o` that pushes elements into the array using the spread operator (`...`). The test cases then execute the function `n` times, measuring the execution time.

**Options being compared**

The three options being compared are:

1. **`var`**: A legacy variable declaration that hoists the variable to the top of its scope.
2. **`let`**: A block-scoped variable declaration that allows re-declaration within the same scope.
3. **`const`**: A constant variable declaration that also hoists the variable, but cannot be reassigned.

**Pros and Cons**

1. **`var`**:
	* Pros: Simple, widely supported, and easy to use in older JavaScript environments.
	* Cons: Hoisting can lead to unexpected behavior due to scope issues, and it's no longer recommended for new code.
2. **`let`**:
	* Pros: Block-scoped, allowing re-declaration within the same scope, and provides a safer alternative to `var`.
	* Cons: Not supported in older JavaScript environments (pre ES6).
3. **`const`**:
	* Pros: Provides immutability and is thread-safe.
	* Cons: Can be restrictive if not used carefully, as it prevents re-assignment.

**Library usage**

None of the test cases use any external libraries. The only library mentioned in the benchmark result is `Safari`, which indicates that the tests are being run on a mobile Safari browser.

**Special JavaScript features or syntax**

The test uses the spread operator (`...`) to push elements into the array, which is a feature introduced in ECMAScript 2015 (ES6). This ensures that the test results accurately reflect the performance of these variables in modern JavaScript environments.

**Other alternatives**

In the past, other variable declarations were used in JavaScript:

* **`function`**: An older variable declaration that can only be assigned a value once.
* **`var with init`**: A variation of `var` that initializes the variable at declaration time, but still has hoisting issues.

However, these alternatives are no longer commonly used and have been largely replaced by `let`, `const`, and other modern features.

Related benchmarks:

var vs let vs const (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):