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getElementById + getElementByClassName vs querySelector
(version: 0)
Benchmark.js
Comparing performance of:
getElementById + getElementByClass vs querySelector
Created:
6 years ago
by:
Guest
Go to the latest result
HTML Preparation code:
<div id="testElement"> <div class="testElementChild"></div> <div class="testElementChild"></div> <div class="testElementChild"></div> <div class="testElementChild"></div> <div class="testElementChild"></div> </div>
Tests:
getElementById + getElementByClass
var el = document.getElementById('testElement'); var children = el.getElementsByClassName('testElementChild'); var length = children.length;
querySelector
var el = document.querySelector('#testElement .testElementChild'); var length = el.length;
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
Fork
Test case name
Result
getElementById + getElementByClass
querySelector
Fastest:
N/A
Slowest:
N/A
Latest run results:
Run details:
(Test run date:
one year ago
)
User agent:
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0
Browser/OS:
Firefox 128 on Windows
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Embed Benchmark Result
<iframe src="https://measurethat.net/Embed?id=606820" width="100%" height="500px"></iframe>
getElementById + getElementByClass
5.7M/s
querySelector
1.1M/s
View exact numbers
Test name
Executions per second
✓
getElementById + getElementByClass
5,653,047 Ops/sec
querySelector
1,096,920 Ops/sec
Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's dive into the explanation of the provided JSON benchmark. **Benchmark Definition** The test compares two approaches for selecting elements in HTML documents: 1. `getElementById + getElementByClassName` (or, more accurately, `getElementsByTagName` followed by `getElementsByClassName`) 2. `querySelector` **What are we testing?** We're measuring the performance of these two methods on a specific HTML document with multiple child elements. **Options compared** The options being compared are: * Using `document.getElementById` and then `el.getElementsByClassName` to get all elements with a specific class. * Using `document.querySelector` to select an element based on a CSS selector (in this case, `#testElement .testElementChild`). **Pros and Cons of each approach** 1. **getElementById + getElementByClassName** * Pros: + Easy to implement and understand for beginners. + Works well for single-element scenarios or when the element is not present in the DOM. * Cons: + Inefficient for large datasets, as it uses a DOM traversal approach that can be slow. + Not suitable for dynamic content or elements with multiple classes. 2. **querySelector** * Pros: + More efficient than `getElementById + getElementByClassName`, especially for larger datasets. + Supports CSS selectors, making it easier to select complex patterns. * Cons: + Can be more challenging to understand and implement, especially for beginners. + May require additional dependencies or polyfills (e.g., for older browsers). **Library/Tool usage** In this benchmark, `querySelector` is implemented by the browser's JavaScript engine. However, if you're using a library like jQuery, you might use its `$(selector)` equivalent to select elements. **Special JS feature/syntax** None are mentioned in this benchmark. **Other alternatives** Additional approaches for selecting elements include: * Using `getElementsByTagName` and then filtering the results. * Using `querySelectorAll` (similar to `querySelector`, but returns all matching elements). * Using a library like jQuery, which provides its own set of selectors and methods for working with elements. * Using a framework like React or Angular, which often provide their own built-in DOM management systems. **Benchmark preparation code** The provided HTML document contains an `<div>` element with the ID `testElement` and multiple child elements with the class `testElementChild`. The JavaScript script prepares two variables: `el` (the selected element) and `children` (an array of child elements). **Individual test cases** There are two test cases: 1. `getElementById + getElementByClass`: This test case uses `document.getElementById` to select the `testElement` and then `getElementsByClassName` to get all child elements with the class `testElementChild`. 2. `querySelector`: This test case uses `document.querySelector` to select an element based on a CSS selector (`#testElement .testElementChild`) and then retrieves its length. The benchmark results show the number of executions per second for each test case, indicating their relative performance on this specific HTML document.
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