Benchmark: const vs var vs let fork

Tests:

const num
const a = 12109203910293019120392342342; const b = 12109203910293019120392342342; const c = 12109203910293019120392342342; const d = 12109203910293019120392342342;
const string
const a = "12109203910293019120392342342";
var num
var a = 12109203910293019120392342342; var b = 12109203910293019120392342342; var c = 12109203910293019120392342342; var d = 12109203910293019120392342342;
var string
var a = "12109203910293019120392342342";
let num
let a = 12109203910293019120392342342; let b = 12109203910293019120392342342; let c = 12109203910293019120392342342; let d = 12109203910293019120392342342;
let string
const a = "12109203910293019120392342342";

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
const num
const string
var num
var string
let num
let string

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.125 Safari/537.36

Browser/OS: Chrome 84 on Mac OS X 10.15.6

View result in a separate tab

Test name	Executions per second
const num	852126080.0 Ops/sec
const string	856863360.0 Ops/sec
var num	861220736.0 Ops/sec
var string	861910464.0 Ops/sec
let num	857734592.0 Ops/sec
let string	860402944.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided JSON data represents a benchmark with six test cases, each testing different approaches for variable declarations (const, var, and let).

**Variable Declaration Approaches**

The benchmark tests four variable declaration approaches:

1. **const**: A constant value is assigned to multiple variables.
2. **var**: A variable is declared using the traditional `var` keyword, with multiple assignments.
3. **let**: A variable is declared using the `let` keyword, with multiple assignments.
4. **const fork** (not explicitly tested): This approach is not shown in the provided data, but it's worth mentioning that some browsers might optimize const variables by reusing the same storage location for all assigned values.

**Options Compared**

The benchmark compares the performance of each variable declaration approach:

* **const**: A constant value is assigned to multiple variables.
	+ Pros: Can provide better memory management and less garbage collection overhead.
	+ Cons: Variables declared with `const` cannot be reassigned.
* **var**: A variable is declared using the traditional `var` keyword, with multiple assignments.
	+ Pros: None notable.
	+ Cons: Can lead to performance issues due to scope resolution and reassignment overhead.
* **let**: A variable is declared using the `let` keyword, with multiple assignments.
	+ Pros: More memory efficient than `var`, but slower than `const`.
	+ Cons: Variables declared with `let` are not hoisted like variables in `var`.

**Library and Special Features**

None of the test cases use any external libraries or special JavaScript features. The benchmark focuses solely on testing the performance difference between different variable declaration approaches.

**Other Considerations**

* **Hoisting**: In modern browsers, some variables declared with `const` or `let` are hoisted to the top of their scope, while variables in `var` are not hoisted.
* **Scope Resolution**: The `var` keyword can lead to slower performance due to scope resolution, as the browser needs to resolve the scope of each variable assignment.

**Alternatives**

If you're interested in creating your own JavaScript microbenchmarks or want to explore other approaches, consider using tools like:

* jsperf (now deprecated)
* Benchmark.js
* js-benchmark

These tools provide more advanced features and options for testing different aspects of JavaScript performance.

Related benchmarks:

const vs var vs let fork (version: 0)

Comparing performance of: const num vs const string vs var num vs var string vs let num vs let string

Created: 4 years ago by: Guest

Jump to the latest result

const num

const string

var num

var string

let num

let string

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):