Benchmark: const vs let vs var comparison

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()

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

var

17.1M/s

const

7.5M/s

let

7.0M/s

Fastest: var (2.4x faster)

View exact numbers

✓ var: 17,136,066 ops/sec
• const: 7,477,956 ops/sec
• let: 7,035,706 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

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: 2 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36

Browser/OS: Chrome 128 on Windows

View result in a separate tab

var

23.5M/s

let

8.5M/s

const

7.6M/s

View exact numbers

Test name	Executions per second
✓ var	23,471,994 Ops/sec
let	8,462,191 Ops/sec
const	7,598,854 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into explaining the JavaScript microbenchmark on MeasureThat.net.

**Overview**

The provided JSON represents a benchmark test that compares the performance of three variable declarations in JavaScript: `var`, `let`, and `const`. Each test case has its own script preparation code, which defines a function `g.o` that pushes an array of numbers onto an object's `e` property.

**Options Compared**

The options being compared are:

* `var`: Variable Declaration
* `let`: Let Statement (a newer variable declaration mechanism introduced in ECMAScript 2015)
* `const`: Constant Statement (another new variable declaration mechanism)

These three options have different scoping behaviors, hoisting rules, and memory allocation strategies, which can impact their performance.

**Pros and Cons of Each Approach**

1. **var**: `var` has a function scope, which means its variables are globally accessible within the same function. This can lead to unexpected behavior and memory leaks if not used carefully.
2. **let**: `let` has block scope, which means its variables are only accessible within the block they're declared in (e.g., inside an if statement or a loop). This improves code readability and avoids global variable pollution.
3. **const`: Like `let`, `const` also has block scope and is used to declare variables that don't change value. However, `const` is immutable by default (i.e., its values cannot be reassigned), which can improve performance in certain cases.

**Library Usage**

In the provided benchmark code, there is no explicit library usage mentioned. However, the use of modern JavaScript features like `let`, `const`, and array destructuring (`[1,2,3]`) suggests that the code assumes a JavaScript environment with recent syntax support.

**Special JS Features or Syntax**

There are no specific special JS features or syntaxes used in this benchmark other than what's mentioned above (e.g., block scope, function declarations). The focus is on comparing the performance of different variable declaration mechanisms.

**Other Alternatives**

To measure the performance of JavaScript variables, alternative approaches could include:

* **Timing Function**: Measuring the time taken by a specific piece of code using `Date.now()` or `performance.now()`.
* **Benchmarking Frameworks**: Utilizing dedicated benchmarking frameworks like Benchmark.js, JSPerf, or Microbenchmark to create more complex and nuanced benchmarks.
* ** Profiling Tools**: Using profiling tools like Chrome DevTools' Performance Tab or Node.js built-in profilers to analyze memory allocation and execution times.

Keep in mind that these alternatives might require additional setup and configuration but can provide more comprehensive insights into the performance characteristics of different JavaScript variables.

const vs let vs var comparison (version: 0) Benchmark.js

Comparing performance of: `var vs let vs const`

Created: 2 years ago by: Guest

Go to the latest result

var

let

const

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

const vs let vs var comparison (version: 0) Benchmark.js

Comparing performance of: var vs let vs const

Created: 2 years ago by: Guest

Go to the latest result

var

let

const

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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Comparing performance of: `var vs let vs const`