Benchmark: Bound Symbol.iterator effect on for..of loop performance

Script Preparation code:

var randomArray = [];
for (let i = 0; i < 10000; i++) {
  randomArray[i] = i*i;
}

var set1 = new Set(randomArray);
var set2 = new Set(randomArray);
set2[Symbol.iterator] = set2[Symbol.iterator].bind(set2);

Tests:

native set
for (let item of set1) { if (typeof item !== 'number') { throw new Error('wtf'); } }
set with [Symbol.iterator] modified to a bound function
for (let item of set2) { if (typeof item !== 'number') { throw new Error('wtf'); } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
native set
set with [Symbol.iterator] modified to a bound function

Fastest: N/A

Slowest: N/A

Latest run results:

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark test case and explain what is being tested.

**Benchmark Description**

The test case is designed to measure the performance difference between two approaches:

1. **Native Set**: This approach uses the built-in `Set` object, which automatically handles iteration using its `Symbol.iterator` property.
2. **Modified Set with Bound Symbol.Iterator**: In this approach, the `Symbol.iterator` property of the `Set` object is manually bound to the `Set` instance using the `bind()` method.

**What's being tested?**

The test case is checking how V8 (the JavaScript engine used by Chrome and other browsers) optimizes for...of loops in sets. Specifically, it's testing whether the optimization goes away if the `Symbol.iterator` property is replaced with a bound function.

**Options compared**

Two options are being compared:

1. **Native Set**: This approach uses the built-in `Set` object.
2. **Modified Set with Bound Symbol.Iterator**: In this approach, the `Symbol.iterator` property of the `Set` object is manually bound to the `Set` instance using the `bind()` method.

**Pros and Cons**

* **Native Set**:
	+ Pros: Simple and straightforward implementation.
	+ Cons: Might not be optimized for performance by V8.
* **Modified Set with Bound Symbol.Iterator**:
	+ Pros: Forces V8 to use a specific optimization path, which might improve performance.
	+ Cons: Requires manual binding of the `Symbol.iterator` property, adding complexity to the code.

**Other considerations**

This test case is relevant because it targets a specific optimization in V8. By testing this scenario, the benchmark creators are trying to understand how V8 handles iteration over sets and whether the optimization is robust across different approaches.

**Library and Purpose**

The `Set` object is a built-in JavaScript library that provides a data structure for storing unique values. Its purpose is to allow efficient lookup, insertion, and removal of elements while maintaining uniqueness.

**Special JS Feature or Syntax**

This test case uses the `Symbol.iterator` property, which is a syntax feature introduced in ECMAScript 2015 (ES6). It's used to define a custom iterator protocol for objects. In this case, it's being used to iterate over the set using a...of loop.

**Other alternatives**

There are other ways to implement iteration over sets, such as:

* Using a `forEach()` method with a callback function.
* Creating an array of values from the set and iterating over that array.
* Implementing a custom iterator class.

However, these approaches might not be relevant for this specific benchmark test case.

Related benchmarks:

Bound Symbol.iterator effect on for..of loop performance (version: 0)

It is believed that v8 optimizes for..of loops in some way. Will this optimization goes away if [Symbol.iterator] is replaced to a bound function?

Comparing performance of: native set vs set with [Symbol.iterator] modified to a bound function

Created: 4 years ago by: Guest

Jump to the latest result

native set

set with [Symbol.iterator] modified to a bound function

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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