Benchmark: querySelector vs getElementsByClassName[0] with real dom

HTML Preparation code:

<h1> Hello world</h1>
<h2>Sub title </h2>
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<div class="test"></div><div class="test"></div>

Tests:

querySelector
document.querySelector(".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

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what is tested, compared, and their pros and cons.

**Benchmark Overview**

The MeasureThat.net benchmark compares two ways to select elements from a HTML document in JavaScript: `querySelector` and `getElementsByClassName`. The test creates an HTML page with multiple elements that contain the class "test", simulating a real-world scenario where you might need to find elements based on their class.

**Options Compared**

The options being compared are:

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

These two approaches have different use cases and performance characteristics:

* `querySelector` is more efficient and flexible when selecting elements by a single class or attribute. It returns the first element that matches the selector, making it suitable for scenarios where you know there's only one matching element.
* `getElementsByClassName` returns an array of all elements that contain the specified class name. If you're sure there's only one element with the class, you can use `[0]` to get the first element in the array.

**Pros and Cons**

Here are some pros and cons for each approach:

**querySelector:**

Pros:

* Faster execution time
* More efficient when selecting elements by a single class or attribute
* Returns the first matching element

Cons:

* Returns `null` if no matching element is found
* Limited flexibility (only works with single class or attribute selectors)

**getElementsByClassName:**

Pros:

* Returns all matching elements, not just the first one
* Flexible when selecting elements by multiple classes

Cons:

* Slower execution time compared to `querySelector`
* Returns an array of elements, which might be unnecessary if only one element is expected

**Library and Purpose**

In this benchmark, there are no external libraries used. The test focuses on comparing the built-in JavaScript methods `querySelector` and `getElementsByClassName`.

**Special JS Feature or Syntax**

There's no special JavaScript feature or syntax being tested here. Both `querySelector` and `getElementsByClassName` are standard DOM manipulation APIs.

**Alternative Approaches**

If you need to compare performance between different class names or attribute selectors, you could modify the benchmark to include additional options, such as:

* Using `document.querySelector("class1 class2")`
* Using `document.querySelectorAll(".test .another-class")`

You could also explore using other libraries like jQuery or a custom implementation to see how they perform compared to the built-in JavaScript methods.

**Conclusion**

The MeasureThat.net benchmark provides a useful comparison between two common ways to select elements from an HTML document in JavaScript: `querySelector` and `getElementsByClassName`. Understanding the pros and cons of each approach can help developers choose the most efficient method for their specific use cases.

Latest run results:

Run details: (Test run date: 5 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36

Browser/OS: Chrome 74 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	2556672.2 Ops/sec
getElementsByClassName	2262064.8 Ops/sec

Related benchmarks:

querySelector vs getElementsByClassName[0] with real dom (version: 0)

Slight alteration because querySelector only returns a first element.

Comparing performance of: querySelector vs getElementsByClassName

Created: 5 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 27 days ago):