Benchmark: precise querySelector vs first element of getElementsByClassName

HTML Preparation code:

<div class="test"></div>

Tests:

querySelector
document.querySelector("div.test")
getElementsByClassName
document.getElementsByClassName(".test")[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Safari/605.1.15

Browser/OS: Safari 13 on Mac OS X 10.15.5

View result in a separate tab

Test name	Executions per second
querySelector	3691460.2 Ops/sec
getElementsByClassName	4192492.8 Ops/sec

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

LLMs can make mistakes. Check important info.

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

The benchmark compares two approaches to select an element from HTML:

1. `document.querySelector("div.test")`
2. `document.getElementsByClassName(".test")[0]`

**What are we comparing?**

We're comparing the performance of these two approaches on a single element with class `test`. The difference lies in how they retrieve and return the selected elements.

* `document.querySelector("div.test")` uses the `querySelector` method, which is a more modern and efficient way to select elements. It returns the first matching element from left to right.
* `document.getElementsByClassName(".test")[0]` uses the `getElementsByClassName` method, which returns an array of all elements with the specified class name.

**Options compared:**

We're comparing two options:

1. **`querySelector`**: a modern and efficient way to select elements that returns the first matching element.
2. **`getElementsByClassName`**: an older approach that returns an array of all matching elements.

**Pros and Cons:**

* `querySelector`:
	+ Pros: more efficient, easier to use, less prone to errors (e.g., no need to worry about the index 0).
	+ Cons: not supported in older browsers (pre-IE 9), might not be as fast for large selections.
* `getElementsByClassName`:
	+ Pros: widely supported across browsers, can handle more complex class names.
	+ Cons: slower and less efficient than `querySelector`, more prone to errors.

**Library and purpose:**

In this benchmark, no specific library is used. However, if you're using a library like jQuery or Lodash, they might provide similar functionality for selecting elements.

**Special JS feature or syntax:**

There are no special JavaScript features or syntax used in this benchmark. Both approaches use standard DOM methods.

**Other alternatives:**

If you want to explore other options:

1. **`querySelectorAll`**: returns all matching elements instead of just the first one.
2. **CSS selectors**: can be used with `querySelector` and `querySelectorAll` to select elements based on class, ID, tag name, etc.
3. **Regular expressions**: can be used with `querySelector` and `querySelectorAll` to match patterns in element names or attributes.

Overall, this benchmark helps users understand the performance differences between modern DOM methods (`querySelector`) and older approaches (`getElementsByClassName`). It's a simple yet informative test that highlights the importance of choosing efficient and reliable methods for selecting elements.

Related benchmarks:

precise querySelector vs first element of getElementsByClassName (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 4 years ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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