Benchmark: querySelector vs getElementsByClassName lexlexa

HTML Preparation code:

<div class="card card-slim gl-overflow-hidden">
  <div
    class="card-header gl-display-flex gl-justify-content-space-between panel-empty-heading border-bottom-0"
  >
    <h3
      class="card-title h5 position-relative gl-my-0 gl-display-flex gl-align-items-center gl-h-7"
    >
      <a
        id="user-content-related-issues"
        aria-hidden="true"
        href="#related-issues"
        class="gl-link anchor position-absolute gl-text-decoration-none"
      ></a>
      Linked issues
      <a
        aria-label="Read more about related issues"
        rel="noopener"
        target="_blank"
        href="/help/user/project/issues/related_issues"
        class="gl-link gl-display-flex gl-align-items-center gl-ml-2 gl-text-gray-500"
        ><svg
          data-testid="question-icon"
          aria-hidden="true"
          class="gl-icon s12"
          role="text"
        >
          <use
            href="/assets/icons-2fb014ce49a3e87b1e47aae4b8adfa35e6b59f49e1474a18a2518ad2285bce08.svg#question"
          ></use>
          </svg></a>
      <div class="gl-display-inline-flex">
        <div
          class="js-related-issues-header-issue-count gl-display-inline-flex gl-mx-5"
        >
          <span class="gl-display-inline-flex gl-align-items-center"
            ><svg
              data-testid="issues-icon"
              aria-hidden="true"
              class="gl-mr-2 gl-text-gray-500 gl-icon s16"
            >
              <use
                href="/assets/icons-2fb014ce49a3e87b1e47aae4b8adfa35e6b59f49e1474a18a2518ad2285bce08.svg#issues"
              ></use>
            </svg>
            0
          </span>
        </div>
        <button
          data-qa-selector="related_issues_plus_button"
          aria-label="Add a related issue"
          type="button"
          class="btn js-issue-count-badge-add-button btn-default btn-md gl-button btn-icon"
        >

          <svg
            data-testid="plus-icon"
            aria-hidden="true"
            class="gl-button-icon gl-icon s16"
          >
            <use
              href="/assets/icons-2fb014ce49a3e87b1e47aae4b8adfa35e6b59f49e1474a18a2518ad2285bce08.svg#plus"
            ></use>
          </svg>

        </button>
      </div>
    </h3>
  </div>
  <div class="linked-issues-card-body bg-gray-light">
  </div>
</div>

Tests:

querySelector
document.querySelector('.card-header').querySelector('.gl-mx-5')
getElementByClassName
document.getElementsByClassName('card-header')[0].getElementsByClassName('gl-mx-5')[0]

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementByClassName

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.

Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net.

**Benchmark Overview**

The benchmark compares two ways to select elements in HTML: `document.querySelector` and `document.getElementsByClassName`. The test case uses an HTML structure with a single `<div>` element that contains another `<div>` element with class `card-header` and another one with class `gl-mx-5`.

**Options Compared**

There are two options compared:

1. **`document.querySelector('.card-header').querySelector('.gl-mx-5')`**: This code uses the `querySelector` method to select the first element with class `card-header`, and then uses `querySelector` again to select the first element with class `gl-mx-5` within that selected element.
2. **`document.getElementsByClassName('card-header')[0].getElementsByClassName('gl-mx-5')[0]`**: This code uses the `getElementsByClassName` method to select all elements with class `card-header`, gets the first one, and then uses `getElementsByClassName` again to select the first element with class `gl-mx-5` within that selected element.

**Pros and Cons of Each Approach**

1. **`document.querySelector('.card-header').querySelector('.gl-mx-5')`**:
	* Pros: More efficient and modern way of selecting elements, as it uses a single method to find the desired element.
	* Cons: May not work in older browsers that don't support `querySelector`.
2. **`document.getElementsByClassName('card-header')[0].getElementsByClassName('gl-mx-5')[0]`**:
	* Pros: Works in older browsers, as it uses a more traditional method for selecting elements by class name.
	* Cons: Less efficient and less modern way of selecting elements.

**Library Used**

None are explicitly mentioned in the benchmark definition. However, `getElementsByClassName` is a standard HTML method for selecting elements by class name.

**Special JavaScript Features or Syntax**

None are used in this benchmark.

**Other Considerations**

When choosing between these two approaches, consider the following:

* If you need to support older browsers that don't support `querySelector`, use the second approach.
* If you want a more efficient and modern way of selecting elements, use the first approach.
* Be aware that both approaches have some overhead due to the method calls.

**Alternative Approaches**

Other ways to select elements in JavaScript include:

1. **`document.querySelector('[data-qa-selector="card-header"]')`**: This uses an attribute selector to find the desired element.
2. **`document.querySelectorAll('.card-header')[0]`**: This uses `querySelectorAll` to select all elements with class `card-header` and then gets the first one.

These alternatives may have different performance characteristics and are suitable for specific use cases.

Related benchmarks:

querySelector vs getElementsByClassName lexlexa (version: 0)

Comparing performance of: querySelector vs getElementByClassName

Created: 5 years ago by: Guest

Jump to the latest result

querySelector

getElementByClassName

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):