Benchmark: getElementsByClass vs. querySelector

HTML Preparation code:

<div class="wrapper">
  <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
</div>
<script src='https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js'></script>

Tests:

queryselector
document.querySelector(".item");
class by name
document.getElementsByClassName("test");

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
queryselector
class by name

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

**What is being tested?**

The provided JSON represents two microbenchmarks that test the performance of JavaScript's `getElementsByClass` and `querySelector` methods.

**Options compared:**

Two options are being compared:

1. **`document.querySelector(".item")`**: This method uses a CSS selector to select elements with the class "item" by value.
2. **`document.getElementsByClassName("test")`**: This method returns an HTMLCollection of elements with the exact class name "test".

**Pros and Cons:**

* **`document.querySelector(".item")`**:
	+ Pros:
		- Faster because it only needs to look up a single class name, rather than checking for multiple classes.
		- More flexible since it can be used with different CSS selectors (e.g., `.item span`, `.item .inner`).
	+ Cons:
		- May not work as expected in older browsers or those with limited CSS support.
* **`document.getElementsByClassName("test")`**:
	+ Pros:
		- Works consistently across all modern browsers and versions of Internet Explorer.
	+ Cons:
		- Slower because it needs to check for multiple classes, which can lead to slower performance.
		- Less flexible since only exact class names are supported.

**Library usage:**

Neither benchmark uses a specific library, but `querySelector` relies on the W3C CSS Selectors API, which is widely supported in modern browsers. `getElementsByClass`, on the other hand, is a proprietary method provided by Internet Explorer and its clones (e.g., Firefox, Chrome).

**Special JS features or syntax:**

Neither benchmark uses any special JavaScript features or syntax beyond standard ES5/ES6 syntax.

**Other alternatives:**

For faster and more flexible DOM querying:

1. **`document.querySelectorAll(".item")`**: This method returns a NodeList of elements matching the specified CSS selector.
2. **`Element.prototype.querySelector` and `Element.prototype.querySelectorAll`**: These methods, introduced in ECMAScript 2015 (ES6), provide a modern alternative to `querySelector` and `getElementsByClassName`.

For performance-critical applications:

1. **Use a custom implementation** that takes advantage of browser-specific optimizations or your own algorithms.
2. **Consider using a library like jQuery**, which provides optimized DOM querying methods.

Keep in mind that the best approach depends on your specific use case, target browsers, and performance requirements.

Related benchmarks:

getElementsByClass vs. querySelector (version: 0)

Comparing performance of: queryselector vs class by name

Created: 7 years ago by: Guest

Jump to the latest result

queryselector

class by name

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):