Benchmark: querySelector() vs getElementsByClassName()[0]

HTML Preparation code:

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

Tests:

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

Historical Performance Data aggregated from 12 community runs

Desktop Results:

Chrome 6 runs

querySelector

12.3M/s

getElementsByClassName

9.7M/s

Fastest: querySelector (1.3x faster)

View exact numbers

✓ querySelector: 12,325,139 ops/sec
• getElementsByClassName: 9,747,610 ops/sec

Firefox 6 runs

getElementsByClassName

4.2M/s

querySelector

3.4M/s

Fastest: getElementsByClassName (1.2x faster)

View exact numbers

✓ getElementsByClassName: 4,202,180 ops/sec
• querySelector: 3,373,237 ops/sec

Results show median performance across all community submissions. Run this benchmark yourself to verify on your device.

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: 29 days ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:152.0) Gecko/20100101 Firefox/152.0

Browser/OS: Firefox 152 on Windows

View result in a separate tab

getElementsByClassName

3.7M/s

querySelector

3.6M/s

View exact numbers

Test name	Executions per second
✓ getElementsByClassName	3,702,019 Ops/sec
querySelector	3,612,163 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 world of MeasureThat.net and explore what's being tested in this specific benchmark.

**What is being tested?**

The provided JSON represents a JavaScript microbenchmark that compares two DOM query methods: `document.querySelector()` and `document.getElementsByClassName()[0]`. The benchmark aims to measure which method is faster and more efficient for selecting an element by its class name.

**Options compared:**

Two options are being compared:

1. `document.querySelector(".test")`: This method selects the first element in the DOM tree that matches the specified CSS selector (in this case, `.test`).
2. `document.getElementsByClassName("test")[0]`: This method retrieves an array of all elements in the DOM tree that match the specified class name (`"test"`), and then returns the first element from that array.

**Pros and Cons:**

* **`document.querySelector(".test")`:**
	+ Pros:
		- More efficient, as it only needs to traverse a single element from the DOM tree.
		- Can be more selective in terms of CSS selectors, allowing for finer-grained selection.
	+ Cons:
		- May not work if the element is dynamically generated or has multiple matches.
* **`document.getElementsByClassName("test")[0]`:**
	+ Pros:
		- Works even if there are multiple elements with the same class name.
	+ Cons:
		- Requires iterating over all matching elements to get the first one, which can be slower for large datasets.

**Library and purpose:**

There is no specific library mentioned in this benchmark. The methods being compared are part of the native DOM API provided by web browsers.

**Special JS features or syntax:**

None are explicitly used in this benchmark.

**Alternative approaches:**

Other alternatives to compare could include:

* Using `document.querySelector` with a more complex CSS selector (e.g., `.test > span`) to see if it outperforms the simple class name query.
* Adding additional elements with different classes and using `getElementsByClassName` to see how its performance scales with multiple matches.
* Comparing `querySelector` and `getElementsByClassName` against other libraries or frameworks that provide similar functionality (e.g., jQuery).

Keep in mind that these alternatives would require modifying the benchmark JSON and adding new test cases.

querySelector() vs getElementsByClassName()[0] (version: 0)

Comparing performance of: `querySelector vs getElementsByClassName`

Created: 7 years ago by: Guest

Go to the latest result

querySelector

getElementsByClassName

Historical Performance Data aggregated from 12 community runs

Desktop Results:

Chrome 6 runs

Firefox 6 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

querySelector() vs getElementsByClassName()[0] (version: 0)

Comparing performance of: querySelector vs getElementsByClassName

Created: 7 years ago by: Guest

Go to the latest result

querySelector

getElementsByClassName

Historical Performance Data aggregated from 12 community runs

Desktop Results:

Chrome 6 runs

Firefox 6 runs

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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

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Comparing performance of: `querySelector vs getElementsByClassName`