Benchmark: Multiplying lists of vectors - with or without declaration

Script Preparation code:

var N = 1000000;

var vectors = [];
var vector;
for (var i = 0, li=N; i < li; ++i) {
	vectors.push( {x:Math.random(), y:Math.random(), z:Math.random()} );
}

Tests:

with duplicate declaration
var vector; for (var i = 0, li=vectors.length; i < li; ++i) { vector = vectors[i]; vector.x = 2 * vector.x; vector.y = 2 * vector.y; vector.z = 2 * vector.z; }
without duplicate declaration
for (var i = 0, li=vectors.length; i < li; ++i) { vector = vectors[i]; vector.x = 2 * vector.x; vector.y = 2 * vector.y; vector.z = 2 * vector.z; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
with duplicate declaration
without duplicate declaration

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark is designed to measure the performance of JavaScript engines in executing a simple loop that iterates over an array of vectors, multiplying each vector by 2.

**Test Cases**

There are two test cases:

1. **"with duplicate declaration"`**: This test case uses a `var` declaration inside the loop, which means the variable `vector` is redeclared on each iteration.
2. **"without duplicate declaration"`**: This test case does not use a `var` declaration inside the loop, so the variable `vector` is only declared once.

**Comparison**

The two test cases are compared to see how they affect the performance of the JavaScript engine. The idea behind this comparison is to understand how the scope and redeclaration of variables impact the execution time of the benchmark.

**Pros and Cons of Each Approach**

1. **"with duplicate declaration"`**:
	* Pros: Can help catch issues related to variable hoisting or scoping.
	* Cons: May introduce unnecessary overhead due to redeclaration, which can lead to slower performance.
2. **"without duplicate declaration"`**:
	* Pros: Avoids the potential overhead of redeclaring variables on each iteration.
	* Cons: May make it harder to catch issues related to variable scope or hoisting.

**Other Considerations**

The benchmark also considers the use of a library, which is not explicitly mentioned. However, we can infer that some libraries might be using techniques like caching or memoization to optimize performance in loops. In this case, the `vectors` array is created on the fly, and its elements are accessed without any caching.

**Special JavaScript Feature**

There is no special JavaScript feature being tested here. The benchmark focuses on the basic execution of a simple loop with variable declarations.

**Alternatives**

If you were to rewrite this benchmark, you might consider alternatives like:

* Using `let` or `const` instead of `var`, which would avoid redeclaration issues.
* Adding more test cases that cover different scenarios, such as using `let` or `const` without the loop or with more complex logic inside the loop.
* Including additional metrics, such as memory usage or CPU utilization, to gain a deeper understanding of the performance characteristics.

In summary, this benchmark is designed to highlight the impact of variable declarations on JavaScript engine performance. By comparing two test cases with different approaches to redeclaration, it helps identify which approach is more efficient and effective for executing loops in JavaScript code.

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.1 Safari/605.1.15

Browser/OS: Safari 16 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
with duplicate declaration	17.8 Ops/sec
without duplicate declaration	2.0 Ops/sec

Related benchmarks:

Multiplying lists of vectors - with or without declaration (version: 1)

Comparing performance of: with duplicate declaration vs without duplicate declaration

Created: 8 years ago by: Registered User

Jump to the latest result

with duplicate declaration

without duplicate declaration

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 26 days ago):