Benchmark: GetElementByClassName vs GetElementById

HTML Preparation code:

<html>
  <body>
    <div class="test2"></div>
    <div id="test"></div>
  </body>
</html>

Tests:

By Class
document.getElementsByClassName('test2')
By Id
document.getElementById('test')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
By Class
By Id

Fastest: N/A

Slowest: N/A

Latest run results:

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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 JavaScript microbenchmarks on MeasureThat.net.

**What is tested?**

The provided JSON represents a benchmark test that compares two methods for retrieving HTML elements: `getElementsByClassName` and `getElementById`. The test creates an HTML document with two div elements, one with a class attribute (`class="test2"`) and another with an id attribute (`id="test"`). The benchmark measures the execution time of each method to retrieve all elements that match the specified criteria.

**Options compared**

The two options being compared are:

1. **`getElementsByClassName`**: This method returns a live HTMLCollection object containing all elements that have the specified class name.
2. **`getElementById`**: This method returns a single element with the specified id attribute, or null if no such element is found.

**Pros and Cons of each approach**

* `getElementsByClassName`:
	+ Pros: Can be more efficient for retrieving multiple elements with the same class name, as it only needs to traverse the DOM once.
	+ Cons: May return a live collection that changes when the DOM changes (e.g., when an element is added or removed), which can lead to unexpected behavior in some cases.
* `getElementById`:
	+ Pros: Returns a single, predictable result, making it easier to reason about the code.
	+ Cons: Requires traversing the DOM for each query, which can be slower than `getElementsByClassName`.

**Other considerations**

In modern JavaScript and HTML5, the difference in performance between these two methods is often negligible. However, if you need to retrieve multiple elements with the same class name or if you're working with a large dataset, `getElementsByClassName` might be a better choice.

**Library usage**

There is no external library used in this benchmark test.

**Special JS features or syntax**

None are mentioned in the provided JSON. However, it's worth noting that MeasureThat.net supports various JavaScript features and libraries, such as ES6 promises, async/await, and Web Workers, which can be enabled by modifying the "Script Preparation Code" field in the benchmark definition.

**Other alternatives**

If you need to compare other methods for retrieving HTML elements or want more flexibility in your benchmarking setup, consider exploring alternative approaches:

* Use `querySelectorAll` instead of `getElementsByClassName`, which returns a DOM NodeList and provides better support for CSS selectors.
* Experiment with `document.querySelector` instead of `getElementById`, which can be more efficient for retrieving single elements using CSS selectors.
* Consider using other benchmarking tools or frameworks, such as WebPageTest, BrowserStack, or jsPerf (now defunct), to compare performance in different browsers and environments.

Related benchmarks:

GetElementByClassName vs GetElementById (version: 0)

Comparing performance of: By Class vs By Id

Created: 7 years ago by: Guest

Jump to the latest result

By Class

By Id

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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