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querySelectorAll vs. getElementsByClassName with spread
(version: 0)
Comparing performance of:
querySelectorAll vs getElementsByClassName
Created:
5 years ago
by:
Guest
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HTML Preparation code:
<div class="test"></div> <div class="test"></div> <div class="test"></div>
Tests:
querySelectorAll
document.querySelectorAll(".test").forEach(item => console.log(item))
getElementsByClassName
[...document.getElementsByClassName("test")].forEach(item => console.log(item))
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
querySelectorAll
getElementsByClassName
Fastest:
N/A
Slowest:
N/A
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Autogenerated LLM Summary
(model
gemma2:9b
, generated one year ago):
This benchmark compares two ways to select HTML elements: `querySelectorAll` and `getElementsByClassName`. Both methods aim to retrieve elements with a specific class ("test" in this case). Let's break down each approach: **1. `querySelectorAll(".test")`:** * **Description:** This uses the powerful `querySelectorAll` method, which accepts a CSS selector as its argument. It returns a NodeList (a collection of HTML elements) matching the selector. The benchmark then iterates over this list using `forEach`, logging each element to the console. * **Pros:** * **Powerful and Flexible:** Supports complex CSS selectors, allowing for more precise element selection. * **Live Updates:** The returned NodeList updates automatically if the DOM changes, making it suitable for situations where elements are added or removed dynamically. * **Cons:** Can be slower than `getElementsByClassName` for simple class-based selections due to its generality. **2. `[...document.getElementsByClassName("test")]`:** * **Description:** This approach utilizes `getElementsByClassName`, which returns a live HTMLCollection of elements with the specified class name. The spread syntax (`...`) is used to convert this collection into an array, allowing for easy iteration with `forEach`. * **Pros:** * **Performance:** Generally faster than `querySelectorAll` when dealing with simple class-based selections because it's optimized specifically for this task. * **Cons:** Less flexible; only handles class-based selection and cannot utilize complex CSS selectors like `querySelectorAll`. **Other Considerations:** * **Benchmark Context:** The benchmark results depend on the browser, device, and other factors. It's crucial to run benchmarks in various environments to ensure accurate performance comparisons. * **Alternatives:** There are alternative libraries like jQuery that provide methods for element selection. However, for basic tasks, native DOM APIs like `querySelectorAll` and `getElementsByClassName` are often sufficient and performant. In this specific case, the benchmark shows that `querySelectorAll` is slightly faster on average, but the performance difference isn't massive. The choice between the two often boils down to the complexity of your selector needs.
Related benchmarks:
querySelector() vs getElementsByClassName()[0]
getElementsByClassName()[0] vs querySelectorAll
querySelector versus getElementsByClassName
[Fixed] querySelectorAll vs. getElementsByClassName
querySelector vs getElementsByClassName with proper utilization
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