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

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0

Browser/OS: Firefox 128 on Windows

View result in a separate tab

Test name	Executions per second
getElementById + getElementByClass	5653047.0 Ops/sec
querySelector	1096920.4 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 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.

Related benchmarks:

getElementById + getElementByClassName vs querySelector (version: 0)

Comparing performance of: getElementById + getElementByClass vs querySelector

Created: 6 years ago by: Guest

Jump to the latest result

getElementById + getElementByClass

querySelector

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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