Benchmark: querySelector vs get First Element By Class Name

HTML Preparation code:

<div class="test"></div>
<div class="test2"></div>
<div class="test3"></div>
<div class="test4"></div>

Tests:

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

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByClassName[0]

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36

Browser/OS: Chrome 83 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	1670700.0 Ops/sec
getElementsByClassName[0]	1092603.1 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's being tested.

**Benchmark Overview**

The benchmark compares two approaches to select an element by class name: `document.querySelector()` and `document.getElementsByClassName()[0]`. Both methods are used to retrieve the first element with the specified class name from a HTML document.

**Options Compared**

There are only two options being compared:

1. **`document.querySelector(".test")`**: This method uses the `querySelector` function, which returns the first element that matches the specified selector (in this case, an element with the class "test").
2. **`document.getElementsByClassName("test")[0]`**: This method uses the `getElementsByClassName` function to retrieve all elements with the specified class name and then returns the first one in the resulting array.

**Pros and Cons of Each Approach**

1. **`document.querySelector(".test")`**:
	* Pros:
		+ More concise and expressive syntax.
		+ Handles more complex selectors, including attribute values and pseudo-classes.
		+ Returns the first matching element, which is what we want in this benchmark.
	* Cons:
		+ May be slower than `getElementsByClassName` for very large numbers of elements or deeply nested HTML structures.
2. **`document.getElementsByClassName("test")[0]`**:
	* Pros:
		+ Can return multiple elements if there are multiple elements with the specified class name, whereas `querySelector` would stop at the first match.
	* Cons:
		+ Requires more code to get the desired result (by indexing into the array returned by `getElementsByClassName`).
		+ May be slower than `querySelector` due to the overhead of creating and searching an array of elements.

**Library Used**

In this benchmark, no specific JavaScript library is used beyond the standard DOM APIs (`document`, `querySelector`, `getElementsByClassName`). However, if we were using a more advanced library like jQuery, it would likely provide an alternative implementation for these methods.

**Special JS Features or Syntax**

None are mentioned in the provided code snippet. If any special features or syntax were involved (e.g., ES6 classes, Promises, async/await), they would not be relevant to this specific benchmark.

**Alternatives**

Other alternatives for selecting elements by class name might include:

* Using `document.querySelector()` with a more complex selector (e.g., `.test > div`, `[data-test="text"]`)
* Using `getElementsByClassName()` in combination with other DOM methods (e.g., `querySelectorAll()`, `getElementsByTagName()`)
* Using CSS selectors with the `querySelector()` method
* Using a library like jQuery or React's `useRef`/`useCallback` hooks to handle element selection and manipulation.

Keep in mind that these alternatives might not be as straightforward or efficient as the original implementation compared in this benchmark.

Related benchmarks:

querySelector vs get First Element By Class Name (version: 0)

Comparing performance of: querySelector vs getElementsByClassName[0]

Created: 4 years ago by: Guest

Jump to the latest result

querySelector

getElementsByClassName[0]

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):