Benchmark: getElementById vs querySelector (class)

HTML Preparation code:

<div id="testElement" class="testClass"></div>

Tests:

getElementById
var el = document.getElementById('testElement'); var className = el.className;
querySelector (class)
var el = document.querySelector('.testClass'); var className = el.className;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById
querySelector (class)

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/115.0.0.0 Safari/537.36

Browser/OS: Chrome 115 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
getElementById	5497740.0 Ops/sec
querySelector (class)	4002229.2 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and explain what is being tested.

**Benchmark Overview**

The benchmark compares the performance of two ways to get an HTML element by its class name: `getElementById` and `querySelector`. The goal is to determine which method is faster in this specific scenario.

**Options Compared**

Two options are compared:

1. `getElementById`: This method retrieves an element by its ID, and then uses the `className` property to access the class name.
2. `querySelector`: This method directly searches for elements with a specified class name.

**Pros and Cons**

* **`getElementById`**:
	+ Pros: Well-supported in older browsers, can be useful if you need to get an element by its ID regardless of class names.
	+ Cons: Requires getting the element's ID first, which can be slower than `querySelector`.
* **`querySelector`**:
	+ Pros: Directly searches for elements by class name, potentially faster and more efficient.
	+ Cons: May not work in older browsers that don't support this method.

**Other Considerations**

* The benchmark assumes that the element with the specified class name exists in the HTML document. If it doesn't, `querySelector` will return `null`, while `getElementById` might throw an exception or return a different value.
* The benchmark uses Chrome 115 as the browser, which supports both methods. Results may vary across other browsers and versions.

**Library and Purpose**

None of the tests use any libraries explicitly mentioned in the provided JSON.

**Special JS Feature or Syntax**

The test doesn't mention any special JavaScript features or syntax beyond standard ECMAScript syntax. If there were any specific syntax features like async/await, promises, or modern ES6+ features, they would likely be used to simplify the benchmark code or make it more representative of real-world scenarios.

**Alternatives**

To compare the performance of `getElementById` and `querySelector`, you could also consider using other methods, such as:

* Using `querySelectorAll` with the `class` attribute instead of `querySelector`.
* Comparing the performance of `getElementsByTagName` against `querySelector` or `querySelectorAll`.
* Testing different browser versions or environments to see how support for these methods varies.

To create a new benchmark on MeasureThat.net, you would need to provide similar JSON data, including the test definition and individual test cases. You can choose from various template options to get started with creating your own benchmarks.

Related benchmarks:

getElementById vs querySelector (class) (version: 0)

Comparing performance of: getElementById vs querySelector (class)

Created: 4 years ago by: Guest

Jump to the latest result

getElementById

querySelector (class)

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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