Benchmark: const vs let vs var vs sloppy

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

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

var

27.1M/s

let

7.3M/s

const

6.4M/s

sloppy

2.5M/s

Fastest: var (10.8x faster)

View exact numbers

✓ var: 27,145,544 ops/sec
• let: 7,344,035 ops/sec
• const: 6,431,654 ops/sec
• sloppy: 2,522,167 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
sloppy

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:139.0) Gecko/20100101 Firefox/139.0

Browser/OS: Firefox 139 on Linux

View result in a separate tab

const

16.2M/s

var

14.8M/s

let

14.4M/s

sloppy

11.0M/s

View exact numbers

Test name	Executions per second
✓ const	16,244,592 Ops/sec
var	14,815,688 Ops/sec
let	14,416,993 Ops/sec
sloppy	10,983,544 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll explain the benchmark being tested on MeasureThat.net.

**What is being tested?**

The provided benchmark tests the performance difference between four JavaScript variable scoping mechanisms: `var`, `let`, `const`, and "sloppy" (which is a non-standard, older syntax). The benchmark measures how many executions per second each variable scope allows for in a specific JavaScript function.

**Options being compared:**

1. **`var`**: The traditional variable scoping mechanism in JavaScript, where variables are scoped to the entire function.
2. **`let`**: A newer variable scoping mechanism introduced in ES6 (ECMAScript 2015), which allows block-level scoping and re-declaration.
3. **`const`**: Similar to `let`, but variables with `const` cannot be reassigned.
4. **"sloppy"`: An older syntax, which is no longer supported in modern JavaScript versions. It was used before the introduction of `var`, `let`, and `const`.

**Pros and Cons:**

1. **`var`**: Pros: simple to use, widely supported. Cons: can lead to variable hoisting issues, pollutes global scope.
2. **`let`**: Pros: block-level scoping, allows re-declaration with the same name in a different scope, improves code readability. Cons: not supported in older browsers or environments.
3. **`const`**: Similar pros and cons as `let`, but adds an additional layer of safety against accidental re-assignment.
4. **"sloppy"`**: Pros: none. Cons: outdated syntax, pollutes global scope, can lead to variable hoisting issues.

**Library usage**

In the benchmark code, there is no explicit library mentioned. However, JavaScript's built-in `Array.prototype.push` method is used.

**Special JS feature or syntax**

There are no special features or syntaxes being tested in this benchmark. The only thing being varied is the variable scoping mechanism.

**Other alternatives**

For testing variable scoping mechanisms, you could consider other approaches:

* Using a code analysis tool to analyze and compare the generated machine code for each scope.
* Implementing a Just-In-Time (JIT) compiler or using an existing one that can optimize code based on the scoping mechanism used.
* Creating a test framework that allows users to create their own variable scoping tests.

Keep in mind that MeasureThat.net's approach is more focused on measuring the performance impact of different scoping mechanisms, making it a great resource for understanding how these differences affect execution speed.

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

Comparing performance of: `var vs let vs const vs sloppy`

Created: 3 years ago by: Guest

Go to the latest result

var

let

const

sloppy

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 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 vs sloppy (version: 0) Benchmark.js

Comparing performance of: var vs let vs const vs sloppy

Created: 3 years ago by: Guest

Go to the latest result

var

let

const

sloppy

Historical Performance Data aggregated from 5 community runs

Desktop Results:

Chrome 5 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `var vs let vs const vs sloppy`