Benchmark: var vs let vs const loopy

Tests:

var
const loop=500000; let loopindex = 0; var d=0; var iv = []; for ( ; loopindex<loop; loopindex++ ){ iv.push(loopindex); d = iv[loopindex]+35; if ( d < loopindex+5 ) continue; }
let
const loop=500000; let loopindex = 0; var d=0; let il = []; for ( ; loopindex<loop; loopindex++ ){ il.push(loopindex); d = il[loopindex]+35; if ( d < loopindex+5 ) continue; }
const
const loop=500000; let loopindex = 0; var d=0; const ic = []; for ( ; loopindex<loop; loopindex++ ){ ic.push(loopindex); d = ic[loopindex]+35; if ( d < loopindex+5 ) continue; }

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: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36

Browser/OS: Chrome 111 on Windows

View result in a separate tab

Test name	Executions per second
var	352.3 Ops/sec
let	352.7 Ops/sec
const	352.3 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**What is being tested?**

The provided benchmark compares the performance of three variables in a JavaScript loop: `var`, `let`, and `const`. The test case uses a for loop that iterates 500,000 times, performing some arithmetic operations inside the loop.

**Options compared**

The three options being compared are:

1. **`var`**: A traditional variable declaration in JavaScript.
2. **`let`**: A block-scoped variable declaration introduced in ECMAScript 2015 (ES6).
3. **`const`**: A constant variable declaration, also introduced in ES6.

**Pros and Cons of each approach**

1. **`var`**: The traditional way of declaring variables in JavaScript. However, it has some drawbacks:
	* **Hoisting**: Variables declared with `var` are "hoisted" to the top of their scope, which can lead to unexpected behavior.
	* **Scope**: The variable's scope is function-scoped, not block-scoped.
2. **`let`**: A more modern and safer way of declaring variables in JavaScript:
	* **Block-scoping**: Variables declared with `let` are scoped to the nearest block (e.g., `{}` or `for` loop).
	* **Avoids hoisting**: Variables declared with `let` are not "hoisted" like those with `var`.
3. **`const`**: A constant variable declaration that ensures variables cannot be changed once set:
	* **Immutable**: Variables declared with `const` are immutable, which can lead to more predictable code.
	* **Block-scoping**: Like `let`, variables declared with `const` are scoped to the nearest block.

**Other considerations**

The test case also uses arrays (`iv`, `il`, and `ic`) to store indices, which may affect performance. Additionally, the `continue` statement is used inside the loop, which can lead to some optimizations being bypassed.

**Library usage**

There is no explicit library mentioned in the provided benchmark definition or individual test cases. However, it's worth noting that MeasureThat.net likely uses a JavaScript engine like V8 (used by Chrome) to execute the benchmarks.

**Special JS feature or syntax**

There are no special features or syntaxes used in this benchmark beyond those mentioned above.

**Alternative approaches**

If you wanted to rewrite this benchmark using alternative approaches, here are some options:

1. **Use `let` and `const` with block-scoping**: This approach would avoid the issues associated with `var`, such as hoisting.
2. **Use arrays instead of variables**: If performance is a concern, using arrays to store indices might be a more efficient approach than declaring separate variables for each index.
3. **Profile-guided optimization**: MeasureThat.net likely uses profiling tools to optimize the benchmark for specific use cases or devices.

Keep in mind that these alternatives would require significant changes to the benchmark definition and implementation.

Related benchmarks:

var vs let vs const loopy (version: 0)

Comparing performance of: var vs let vs const

Created: one year ago by: Guest

Jump to the latest result

var

let

const

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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