Benchmark: querySelector vs getElementsByClassName

HTML Preparation code:

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

Tests:

querySelector
document.querySelector(".test")
getElementsByClassName
document.getElementsByClassName(".test")

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: 6 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36

Browser/OS: Chrome 66 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	249093.2 Ops/sec
getElementsByClassName	1983676.2 Ops/sec

Autogenerated LLM Summary (model gemma2:9b, generated 2 months ago):

LLMs can make mistakes. Check important info.

This benchmark compares two methods for selecting HTML elements in JavaScript: `document.querySelector()` and `document.getElementsByClassName()`.

**Method 1:** `document.querySelector(".test")`

* **What it does:** This method finds the *first* element on the page that matches the CSS selector ".test". In this case, it will select the `<div>` with the class "test" within the HTML structure provided.

* **Pros:**
    *  **Simplicity:** It's a single-line call that returns the desired element directly.
    * **Efficiency (often):** If you need only the first matching element, `querySelector` is generally faster because it stops searching once the first match is found.

* **Cons:** 
    * **Single Element:** Only returns *one* element. If there are multiple elements with the class ".test", this method will only return the first one encountered.

**Method 2:** `document.getElementsByClassName(".test")`

* **What it does:** This method finds *all* elements on the page that match the CSS selector ".test". It returns a collection of all matching elements as a NodeList.

* **Pros:**
    * **Multiple Elements:**  Returns a list of *all* matching elements, allowing you to work with them collectively or individually.

* **Cons:**
    * **Performance (sometimes):** Can be slower than `querySelector` if you only need the first element, as it has to search through all potential matches.
    * **Traversing:** You need to iterate through the returned NodeList if you want to access individual elements within the collection.

**Other Considerations:**

* **Context Matters:** The best method depends on your specific use case. If you only need a single element, `querySelector` is often faster and simpler. If you require multiple elements or need to process them collectively, `getElementsByClassName` is more suitable. 
* **Alternatives:**  While not covered in this benchmark, there are other ways to select HTML elements:
    *  **By ID:** `document.getElementById("elementId")` (returns a single element by its unique ID).
    * **By tag name:** `document.getElementsByTagName("tagName")` (returns all elements with a specific tag name).

Let me know if you'd like to delve deeper into any of these aspects!

Related benchmarks:

querySelector vs getElementsByClassName (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 6 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 gemma2:9b, generated 2 months ago):