Benchmark: NodeList loop iterator comparison

HTML Preparation code:

<ul>
</ul>

<ol>
</ol>

Script Preparation code:

const ul = document.querySelector('ul');
const ol = document.querySelector('ul');
for (let i = 0; i < 1000; i++) {
    const li = document.createElement('li')
    li.classList.add(i % 2 === 0 ? 'even' : 'odd')
    ul.appendChild(document.createElement('li'));
    ol.appendChild(document.createElement('li'));
}

var oddListItems = document.querySelectorAll('li.odd');

var anything = [];

Tests:

for ... of
for (const item of oddListItems) { anything.push(item); }
Array.from
Array.from(oddListItems).forEach(item => anything.push(item));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for ... of
Array.from

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:131.0) Gecko/20100101 Firefox/131.0

Browser/OS: Firefox 131 on Ubuntu

View result in a separate tab

Test name	Executions per second
for ... of	54437792.0 Ops/sec
Array.from	19368260.0 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 JavaScript microbenchmark on MeasureThat.net.

**What is being tested?**

The benchmark measures the performance of two approaches for iterating over an array or NodeList: `for ... of` and `Array.from()`. The test case creates 1000 NodeList items (even and odd) in both HTML unordered lists (`ul`) and ordered lists (`ol`). The goal is to push each item into a new empty array called `anything`.

**Options compared**

The two options being compared are:

1. **`for ... of`**: This syntax allows iterating over an iterable object, such as an array or NodeList, without explicitly indexing into it.
2. **`Array.from()`**: This method creates a new array from an iterable object.

**Pros and Cons**

*   `For ... of`:
    *   Pros: Easier to read, less verbose, and more intuitive for many developers.
    *   Cons: May be slower in certain situations due to the overhead of the iterator protocol.
*   `Array.from()`:
    *   Pros: Can be faster because it uses a single method call to create an array from an iterable object.
    *   Cons: More verbose, and may require additional understanding of the `Array.prototype.forEach()` method.

**Library/Function**

In this test case, no specific JavaScript library is used. However, some basic HTML elements like `<ul>`, `<ol>`, and `<li>` are used to create the NodeList.

**Special JS feature/Syntax**

The benchmark uses the new `for ... of` syntax, which was introduced in ECMAScript 2015 (ES6). This syntax allows iterating over an iterable object without explicitly indexing into it. The `Array.from()` method is also a part of ES6 and has been widely adopted.

**Other alternatives**

If `for ... of` or `Array.from()` are not suitable for this use case, other alternatives could be:

*   Manual indexing (`while` loop): Push items into the array using an index variable.
*   `forEach()`: Similar to `Array.from()`, but uses a callback function instead of creating a new array.
*   Custom iterators: Create a custom iterator using the `Iterator` class or a generator function.

These alternatives may have different performance characteristics and syntax requirements, so it's essential to evaluate them based on the specific use case.

Related benchmarks:

NodeList loop iterator comparison (version: 0)

Comparing performance of: for ... of vs Array.from

Created: 3 years ago by: Guest

Jump to the latest result

for ... of

Array.from

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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