Benchmark: getElementById + getElementByClassName vs querySelector

HTML Preparation code:

<div id="testElement">
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
</div>

Tests:

getElementById + getElementByClass
var el = document.getElementById('testElement'); var children = el.getElementsByClassName('testElementChild'); var length = children.length;
querySelector
var el = document.querySelector('#testElement .testElementChild'); var length = el.length;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById + getElementByClass
querySelector

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 dive into the explanation of the provided JSON benchmark.

**Benchmark Definition**

The test compares two approaches for selecting elements in HTML documents:

1. `getElementById + getElementByClassName` (or, more accurately, `getElementsByTagName` followed by `getElementsByClassName`)
2. `querySelector`

**What are we testing?**

We're measuring the performance of these two methods on a specific HTML document with multiple child elements.

**Options compared**

The options being compared are:

* Using `document.getElementById` and then `el.getElementsByClassName` to get all elements with a specific class.
* Using `document.querySelector` to select an element based on a CSS selector (in this case, `#testElement .testElementChild`).

**Pros and Cons of each approach**

1. **getElementById + getElementByClassName**
	* Pros:
		+ Easy to implement and understand for beginners.
		+ Works well for single-element scenarios or when the element is not present in the DOM.
	* Cons:
		+ Inefficient for large datasets, as it uses a DOM traversal approach that can be slow.
		+ Not suitable for dynamic content or elements with multiple classes.
2. **querySelector**
	* Pros:
		+ More efficient than `getElementById + getElementByClassName`, especially for larger datasets.
		+ Supports CSS selectors, making it easier to select complex patterns.
	* Cons:
		+ Can be more challenging to understand and implement, especially for beginners.
		+ May require additional dependencies or polyfills (e.g., for older browsers).

**Library/Tool usage**

In this benchmark, `querySelector` is implemented by the browser's JavaScript engine. However, if you're using a library like jQuery, you might use its `$(selector)` equivalent to select elements.

**Special JS feature/syntax**

None are mentioned in this benchmark.

**Other alternatives**

Additional approaches for selecting elements include:

* Using `getElementsByTagName` and then filtering the results.
* Using `querySelectorAll` (similar to `querySelector`, but returns all matching elements).
* Using a library like jQuery, which provides its own set of selectors and methods for working with elements.
* Using a framework like React or Angular, which often provide their own built-in DOM management systems.

**Benchmark preparation code**

The provided HTML document contains an `<div>` element with the ID `testElement` and multiple child elements with the class `testElementChild`. The JavaScript script prepares two variables: `el` (the selected element) and `children` (an array of child elements).

**Individual test cases**

There are two test cases:

1. `getElementById + getElementByClass`: This test case uses `document.getElementById` to select the `testElement` and then `getElementsByClassName` to get all child elements with the class `testElementChild`.
2. `querySelector`: This test case uses `document.querySelector` to select an element based on a CSS selector (`#testElement .testElementChild`) and then retrieves its length.

The benchmark results show the number of executions per second for each test case, indicating their relative performance on this specific HTML document.

Latest run results:

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

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.5112.124 YaBrowser/22.9.3.894 Yowser/2.5 Safari/537.36

Browser/OS: Yandex Browser 22 on Linux

View result in a separate tab

Test name	Executions per second
getElementById + getElementByClass	2050426.9 Ops/sec
querySelector	1899853.8 Ops/sec

Related benchmarks:

getElementById + getElementByClassName vs querySelector (version: 0)

Comparing performance of: getElementById + getElementByClass vs querySelector

Created: 4 years ago by: Guest

Jump to the latest result

getElementById + getElementByClass

querySelector

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):