Benchmark: querySelector(), id vs class

HTML Preparation code:

<section>
  <div>
    <p id="idName" class="className"></p>
  </div>
</section>

Tests:

id
var id = document.querySelector('#idName');
class
var id = document.querySelector('.className')

Historical Performance Data aggregated from 19 community runs

Desktop Results:

Chrome 19 runs

class

11.7M/s

5.2M/s

Fastest: class (2.3x faster)

View exact numbers

✓ class: 11,739,010 ops/sec
• id: 5,180,680 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
id
class

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/142.0.0.0 Safari/537.36

Browser/OS: Chrome 142 on Mac OS X 10.15.7

View result in a separate tab

class

18.1M/s

8.2M/s

View exact numbers

Test name	Executions per second
✓ class	18,103,946 Ops/sec
id	8,169,902 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated one year 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 two different ways of selecting an HTML element using JavaScript: by its `id` attribute or by its class name. The test case uses a simple HTML structure with an `<p>` tag having both an `id` and a `class` attribute.

**Options being compared**

There are only two options being compared in this benchmark:

1. **`document.querySelector('#idName')`**: This is the traditional way of selecting an element by its `id` attribute.
2. **`document.querySelector('.className')`**: This method selects elements that match any CSS class name, including the one specified.

**Pros and Cons**

**Traditional `id` approach (`document.querySelector('#idName')`)**:

Pros:

* Fast: Selecting an element by its `id` is typically faster than other methods because it's a direct lookup in the DOM.
* Accurate: The `id` attribute is unique to each element, making it easier to identify and select.

Cons:

* Limited scalability: As the number of elements increases, this approach can become slower due to the increased number of elements being checked.
* Limited flexibility: The `id` attribute must be present in the HTML code for this method to work.

**Class-based selection (`document.querySelector('.className')`)**:

Pros:

* Scalable: This approach is more efficient when dealing with a large number of elements because it only checks elements that match the specified class.
* Flexible: The `.className` syntax allows for a wide range of CSS classes, making it easier to style and manage HTML content.

Cons:

* Less accurate: When using class-based selection, multiple elements can match the same class name, leading to slower performance due to increased checking time.

**Library usage**

In this benchmark, no specific JavaScript library is used beyond the built-in `document` object. However, in real-world applications, libraries like jQuery or Lodash might be employed for DOM manipulation and selection.

**Special JS features or syntax**

None are explicitly mentioned in the provided code snippet. However, it's essential to note that modern JavaScript has introduced features like arrow functions (`=>`), async/await syntax (e.g., `async function() { ... }`), and template literals (`${}`) for more concise and readable code.

**Other alternatives**

For selecting elements by class name, other approaches besides using the `document.querySelector()` method include:

* Using a CSS selector library like Sizzle.js or jQuery's `.selector()` method
* Implementing your own custom class-based selection algorithm

Keep in mind that these alternatives might come with additional overhead or complexity.

In summary, this benchmark is designed to measure the performance difference between two common methods for selecting HTML elements using JavaScript: by `id` attribute and by CSS class name.

querySelector(), id vs class (version: 0)

Comparing performance of: `id vs class`

Created: 5 years ago by: Guest

Go to the latest result

id

class

Historical Performance Data aggregated from 19 community runs

Desktop Results:

Chrome 19 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

querySelector(), id vs class (version: 0)

Comparing performance of: id vs class

Created: 5 years ago by: Guest

Go to the latest result

id

class

Historical Performance Data aggregated from 19 community runs

Desktop Results:

Chrome 19 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

Related benchmarks

Comparing performance of: `id vs class`