Benchmark: querySelector vs getElementsByClassName()[0]

HTML Preparation code:

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

Tests:

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

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
query
get

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36

Browser/OS: Chrome 131 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
query	7356066.0 Ops/sec
get	5022825.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark definition and test cases.

**Benchmark Definition:**

The benchmark measures the performance of two JavaScript methods:

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

Both methods are used to select an HTML element with a specific class (`"test"`). The main difference between them is that `querySelector` returns the first matching element, while `getElementsByClassName` returns a live HTMLCollection of all matching elements.

**Options Compared:**

The two options being compared are:

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

These two methods differ in their approach to find and return the selected element(s).

**Pros and Cons:**

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

Pros:

* Returns the first matching element, which is often sufficient for most use cases.
* More efficient than `getElementsByClassName` because it uses a single DOM query instead of iterating over all elements.

Cons:

* May not return any elements if no matches are found (unlike `getElementsByClassName`, which returns an empty collection).
* Can be less readable or maintainable if the class name is complex or has multiple meanings.

**`document.getElementsByClassName("test")[0]`:**

Pros:

* Returns all matching elements, allowing for more flexibility in handling multiple matches.
* Less prone to returning no results if no matches are found (in contrast to `querySelector`, which returns null).

Cons:

* More resource-intensive because it involves iterating over all elements that match the class name.
* Can be slower than `querySelector` due to this iteration.

**Library and Purpose:**

In both test cases, no libraries or external dependencies are explicitly mentioned. However, we can infer that these methods rely on the DOM (Document Object Model) API provided by most modern browsers.

**Special JS Feature/Syntax:**

There's no mention of any special JavaScript features or syntax in this benchmark definition. The focus is solely on comparing two standard DOM query methods.

**Alternatives:**

If you wanted to create a similar benchmark, you could consider other DOM query methods, such as:

1. `document.querySelectorAll(".test")`: This method returns a NodeList (a live HTMLCollection) of all matching elements.
2. `window.getComputedStyle(document.querySelector(".test")).className`: This method uses the `getComputedStyle` function to retrieve the computed style of the first matched element.

Keep in mind that these alternatives may not be as efficient or readable as the methods being compared, and should only be used when necessary.

For creating a new benchmark like this one, consider using a tool like MeasureThat.net itself, which provides an easy-to-use interface for defining benchmarks and comparing performance results.

Related benchmarks:

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

Comparing performance of: query vs get

Created: 6 years ago by: Guest

Jump to the latest result

query

get

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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