Benchmark: let vs const vs var

Tests:

let
let a = "Something"
var
var a = "Something"
const
const a = "Something"

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
let
var
const

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 7 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36 SberBrowser/31.0.0.0

Browser/OS: Chrome 139 on Linux

View result in a separate tab

Test name	Executions per second
let	19530754.0 Ops/sec
var	19997848.0 Ops/sec
const	20027864.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**What is tested?**

The benchmark tests the performance difference between three common variable declaration statements in JavaScript:

1. `let`
2. `var`
3. `const`

These declarations are used to declare variables that can hold values. The main differences between them lie in their scope, hoisting, and reassignment behavior.

**Options compared:**

The benchmark compares the performance of each declaration type:

* `let`: creates a new variable declaration with block scope, which means it is scoped to the nearest curly brace `{`.
* `var`: creates a global or function-scoped variable declaration, which can lead to "variable hoisting" issues.
* `const`: also creates a new variable declaration with block scope, similar to `let`.

**Pros and cons:**

Here's a brief summary of each option:

1. **`let`**:
	* Pros:
		+ Block-scoped, reducing global pollution
		+ Can help catch errors earlier (e.g., trying to reassign a constant)
	* Cons:
		+ May introduce unnecessary overhead due to the creation of a new variable declaration
2. **`var`**:
	* Pros:
		+ Less overhead compared to `let`, as it only declares a single variable without creating a new one
	* Cons:
		+ Global or function-scoped, leading to potential naming conflicts and hoisting issues
3. **`const`**:
	* Pros:
		+ Similar benefits to `let`, with block scope and reduced global pollution
	* Cons:
		+ May also incur the overhead of creating a new variable declaration

It's worth noting that modern JavaScript engines, including those in web browsers, have optimized these declarations to minimize overhead.

**Library:**

None is explicitly mentioned in the provided benchmark data. However, it's likely that the `let`, `var`, and `const` variables are using the built-in JavaScript engine.

**Special JS feature or syntax:**

There doesn't appear to be any special JS features or syntax used in this benchmark. The focus is solely on comparing the performance of different variable declaration statements.

**Other alternatives:**

If you're interested in exploring other aspects of JavaScript performance, here are some alternatives:

* `use strict` mode: enables a stricter syntax and behavior for JavaScript code.
* Object literals (`{}`) vs. function declarations (`function() { }`)
* Array literals (`[]`) vs. array constructors (`Array()`)
* Looping constructs (e.g., `for`, `while`, `do-while`)
* Conditional statements (e.g., `if/else`, `switch`)

These benchmarks and other alternatives can help you understand how different aspects of JavaScript impact performance.

In summary, the MeasureThat.net benchmark compares the performance of `let`, `var`, and `const` variable declarations to determine which one is fastest. The results provide insights into the overhead associated with each declaration type and can be useful for optimizing code that involves these variables.

Related benchmarks:

let vs const vs var (version: 0)

Comparing performance of: let vs var vs const

Created: one year ago by: Guest

Jump to the latest result

let

var

const

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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