Benchmark: Var vs Let vs Const Performance II

Script Preparation code:

var numbers = Array.from({ length: 10_000_000 }, (v, i) => i);

Tests:

Var
for (let i = 0; i < numbers.length; i++) { var number = numbers[i]; }
Let
for (let i = 0; i < numbers.length; i++) { let number = numbers[i]; }
Const
for (let i = 0; i < numbers.length; i++) { const number = numbers[i]; }

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/129.0.0.0 Safari/537.36

Browser/OS: Chrome 129 on Windows

View result in a separate tab

Test name	Executions per second
Var	1.5 Ops/sec
Let	1.5 Ops/sec
Const	1.5 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!

The provided JSON represents a benchmark test for performance comparison between three approaches: `var`, `let`, and `const`. The test is designed to measure the execution speed of a simple loop that iterates over an array of 10 million numbers.

Here's what each option is compared:

1. **Var**: The use of `var` declares a global variable, which is not scoped to the block or function it's declared in. This means that the variable will be hoisted to the top of its scope, and its value will be reset on each iteration of the loop.
2. **Let**: The use of `let` declares a block-scoped variable, which means its scope is limited to the block or function it's declared in. This ensures that the variable is not hoisted and has its own unique lifetime.
3. **Const**: The use of `const` also declares a block-scoped variable, but with one key difference: once initialized, its value cannot be changed.

**Pros and Cons of each approach:**

1. **Var**:
	* Pros: None significant in this context, as it leads to performance issues due to the global scope.
	* Cons: Leads to a lot of performance overhead due to variable hoisting and reassignment on each iteration.
2. **Let**:
	* Pros: Efficient use of block scoping, which reduces performance overhead compared to `var`.
	* Cons: Still incurs some performance overhead due to the need for scoping and lookup.
3. **Const**:
	* Pros: Provides a lightweight way to declare variables that don't change, reducing unnecessary allocations and lookups.
	* Cons: Additional overhead due to constant checks during execution.

The test uses an array of numbers generated using `Array.from()`, which creates a new array with the specified length and fills it with values. This is done using a lambda function that takes two parameters (index `v` and iteration number `i`) and returns `i`.

**Library usage:**

There are no explicit libraries used in this benchmark, as the test relies solely on native JavaScript features.

**Special JS feature/syntax:**

None mentioned explicitly in the provided JSON. However, it's worth noting that modern JavaScript engines often rely on various optimizations and features like Just-In-Time (JIT) compilation, caching, and other compiler optimizations to improve performance.

**Other alternatives:**

If you were to modify this benchmark, some alternative approaches could be explored:

1. **Use a different data structure**: Instead of using an array, consider using a more optimized data structure like a `Map` or a `Set`.
2. **Increase the iteration range**: Increase the number of iterations in the loop to further stress the performance differences between `var`, `let`, and `const`.
3. **Add additional variables**: Introduce additional variables that are reassigned or updated within the loop to simulate more complex scenarios.
4. **Use a different programming language**: Consider rewriting the benchmark using another language, like C++ or Rust, to compare performance characteristics with JavaScript.

Keep in mind that these alternatives would likely alter the fundamental nature of the benchmark and might not directly compare the original `var` vs `let` vs `const` test.

Related benchmarks:

Var vs Let vs Const Performance II (version: 1)

Comparing performance of: Var vs Let vs Const

Created: 2 years ago by: Registered User

Jump to the latest result

Var

Let

Const

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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