Benchmark: let vs var for loop

Tests:

let
for (let i = 0; i < 100000000; i++) {}
var
for (var i = 0; i < 100000000; i++) {}

Historical Performance Data aggregated from 17 community runs

Desktop Results:

Chrome 12 runs

let

25/s

var

25/s

View exact numbers

✓ let: 25 ops/sec
• var: 25 ops/sec

Mobile Results:

Safari 5 runs

var

32/s

let

32/s

View exact numbers

✓ var: 32 ops/sec
• let: 32 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
let
var

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:151.0) Gecko/20100101 Firefox/151.0

Browser/OS: Firefox 151 on Windows

View result in a separate tab

var

10/s

let

9/s

View exact numbers

Test name	Executions per second
✓ var	10 Ops/sec
let	9 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down what's being tested in this JavaScript microbenchmark.

**Benchmark Definition**
The benchmark is designed to compare the performance of two common variable declarations in JavaScript: `let` and `var`. The benchmark specifically tests their usage in a for loop, where the loop iterates 100 million times.

**Options Compared**

There are only two options being compared:

1. **Let**: Uses the `let` keyword to declare variables.
2. **Var**: Uses the `var` keyword to declare variables.

The pros and cons of these approaches are as follows:

* **Let**: The main advantage is that it enforces block scope, which means a variable declared with `let` will only be accessible within its surrounding block (i.e., `{}`). This can help prevent global variable pollution. On the other hand, using `let` might slightly incur a performance penalty compared to `var`.
* **Var**: The main advantage is that it has function scope, which means variables declared with `var` are globally scoped and can be accessed anywhere in the code. However, this also makes them more susceptible to global variable pollution.

**Library Usage**
There doesn't appear to be any external libraries used in this benchmark.

**Special JS Features/Syntax**
None mentioned in this specific benchmark.

Now, let's consider alternative approaches:

* **Arrow Functions**: Instead of using `let` or `var`, the code could use arrow functions (`() => { ... }`) for a concise way to define small functions. However, this would not be directly comparable to the `let` vs `var` debate.
* **Const**: The benchmark doesn't mention const, which is another keyword that enforces block scope and can help prevent global variable pollution.
* **For...of Loop**: Instead of using a traditional for loop (`for (var i = 0; i < 100000000; i++) {}`), the code could use a `for...of` loop (`for (const i of Array(100000000)) {}`). However, this would not be directly comparable to the `let` vs `var` debate.

Other alternatives for benchmarking JavaScript performance include:

* Using a different browser or version.
* Changing the script preparation code or HTML preparation code.
* Adding more test cases with different inputs or scenarios.
* Using a different type of loop (e.g., while, do...while).
* Introducing noise in the input data to simulate real-world usage patterns.

Keep in mind that the results of this benchmark might not be representative for your specific use case. You may need to create new benchmarks tailored to your needs.

let vs var for loop (version: 0)

let vs var for loop

Comparing performance of: `let vs var`

Created: 4 years ago by: Guest

Go to the latest result

let

var

Historical Performance Data aggregated from 17 community runs

Desktop Results:

Chrome 12 runs

Mobile Results:

Safari 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):

let vs var for loop (version: 0)

let vs var for loop

Comparing performance of: let vs var

Created: 4 years ago by: Guest

Go to the latest result

let

var

Historical Performance Data aggregated from 17 community runs

Desktop Results:

Chrome 12 runs

Mobile Results:

Safari 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):

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Comparing performance of: `let vs var`