Benchmark: var vs. const vs. let

Tests:

Var
var varVariable = '';
Const
const constVariable = '';
Let
let letVariable = '';

Historical Performance Data aggregated from 7 community runs

Desktop Results:

Chrome 7 runs

Let

171.0M/s

Var

159.6M/s

Const

158.5M/s

View exact numbers

✓ Let: 170,968,320 ops/sec
• Var: 159,577,456 ops/sec
• Const: 158,508,208 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
Const
Let

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 10 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36 Edg/140.0.0.0

Browser/OS: Chrome 140 on Linux

View result in a separate tab

Var

159.6M/s

Const

153.4M/s

Let

148.0M/s

View exact numbers

Test name	Executions per second
✓ Var	159,577,456 Ops/sec
Const	153,423,296 Ops/sec
Let	147,968,784 Ops/sec

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

LLMs can make mistakes. Check important info.

I'd be happy to help you understand the provided JavaScript microbenchmark.

**Benchmark Definition and Script Preparation Code**

The benchmark definition is a simple JSON object that defines the test scenario. It contains three variables: `var`, `const`, and `let`. These are all variable declarations in JavaScript, used to declare variables with different scoping behavior.

The script preparation code is empty, which means that the benchmark does not require any initialization or setup before running the tests.

**Individual Test Cases**

Each test case represents a single variable declaration, where the variable is assigned an empty string. The three test cases are:

* `Var`: Declares a variable using the traditional `var` keyword.
* `Const`: Declares a constant using the `const` keyword.
* `Let`: Declares a variable using the `let` keyword.

**Options Compared**

The benchmark compares the performance of each variable declaration approach: `var`, `const`, and `let`. The goal is to determine which one is the most efficient in terms of execution speed.

**Pros and Cons of Each Approach**

Here's a brief summary of the pros and cons of each approach:

* **Var**: This approach has been widely used in JavaScript for many years, but it has some performance issues. Variables declared with `var` are function-scoped, which means they can be accessed from anywhere in the function where they were declared. However, this also means that they are subject to hoisting, which can lead to unexpected behavior.
* **Const**: The `const` keyword was introduced in ECMAScript 2015 as a way to declare variables with block scope. This makes it more predictable and efficient than `var`. However, constants cannot be reassigned once they have been declared.
* **Let**: The `let` keyword was also introduced in ECMAScript 2015, along with the `const` keyword. It provides a way to declare variables with block scope, similar to `const`, but can be reassigned.

**Library and Special JS Feature**

None of the test cases use any libraries or special JavaScript features beyond the built-in language syntax.

**Other Considerations**

Some additional considerations when running this benchmark:

* The benchmark only measures the execution speed of assigning a value to a variable. It does not consider other aspects, such as memory allocation or garbage collection.
* The benchmark runs on desktop platforms (Linux), which may affect the results compared to mobile or web browsers.
* The benchmark uses Chrome 118 as the test browser, which may also impact the results.

**Alternatives**

If you're interested in running similar benchmarks, you can explore other microbenchmarking tools and frameworks, such as:

* Benchmark.js
* Microbenchmark
* Jest (with its built-in `microBenchmark` module)
* Mocha (with its built-in `mocha-benchmark` plugin)

Keep in mind that each tool has its own strengths and weaknesses, and may offer different features or customization options.

var vs. const vs. let (version: 2)

Comparing performance of: `Var vs Const vs Let`

Created: 7 years ago by: Registered User

Go to the latest result

Var

Const

Let

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):

var vs. const vs. let (version: 2)

Comparing performance of: Var vs Const vs Let

Created: 7 years ago by: Registered User

Go to the latest result

Var

Const

Let

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 Const vs Let`