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Id vs qs vs qsa
(version: 0)
Comparing performance of:
id vs qs vs qsa
Created:
5 years ago
by:
Guest
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HTML Preparation code:
<div id="foo" class = 'bar'></div>
Tests:
id
var element = document.getElementById("foo"); var i = 1000; while (i--) { element.className = "bar"; }
qs
var element = document.querySelector("#foo"); var i = 1000; while (i--) { element.className = "bar"; }
qsa
var element = document.querySelectorAll(".bar"); var i = 1000; while (i--) { for(let i of element) {i.className = "foo";} }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (3)
Previous results
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Test case name
Result
id
qs
qsa
Fastest:
N/A
Slowest:
N/A
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's break down the provided benchmark and its test cases. **What is being tested?** The benchmark measures the performance of three different ways to select an HTML element: 1. `id`: Using the `document.getElementById` method with an ID selector (`#foo`). 2. `qs`: Using the `document.querySelector` method with a CSS selector (`#foo`). 3. `qsa`: Using the `document.querySelectorAll` method with a CSS selector (`*.bar`) and iterating over the resulting NodeList. **Options compared** The benchmark compares the performance of these three approaches: * **Pros of each approach:** + `id`: Simple and efficient, as it only needs to find one element by ID. + `qs`: Flexible and powerful, as it can select elements using CSS selectors with multiple attributes and pseudo-classes. + `qsa`: Fast for large sets of elements, as it returns a NodeList that can be iterated over. * **Cons of each approach:** + `id`: May not work if the element is dynamically generated or has a unique ID that's not the only one on the page. + `qs`: Can be slower than `id` for simple cases, as it needs to parse the CSS selector. + `qsa`: Returns a NodeList, which can be less efficient than an array for certain operations. **Library and purpose** The benchmark uses the following libraries: * None explicitly mentioned, but the code is written in vanilla JavaScript. However, if we consider the `querySelector` and `querySelectorAll` methods, they are part of the W3C DOM API, which provides a standard way to select elements in HTML documents. These methods are implemented by most modern browsers and are widely supported. **Special JS feature or syntax** The benchmark uses the following special JavaScript features: * The `let` keyword with the `of` operator (ES2015), used in the `qsa` test case. * A `while` loop (no specific version required, but common in older browsers). No other special features are mentioned. **Other alternatives** Some alternative approaches to selecting elements include: * Using `document.body.children` or `document.body.getElementsByTagName('div')`, which return a NodeList-like object. However, these methods have some limitations and are generally less efficient than the methods used in this benchmark. * Using `Element.prototype.querySelectorAll` (a part of the DOM API) instead of `document.querySelectorAll`. The latter is more flexible but also slower for simple cases. In summary, the benchmark measures the performance of three common ways to select elements in HTML documents: using an ID selector (`id`), a CSS selector (`qs`), and a NodeList-like object returned by `querySelectorAll` (`qsa`).
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