Benchmark: multiple querySelector vs new variable

HTML Preparation code:


<div id='main'>
<div id='inner'>
<a id='' href='#' />
</div>
</div>

<div id='insert'></div>

Tests:

multiple querySelector
const main = document.querySelector('div#main'); const inner = main.querySelector('div#inner'); document.querySelector('div#insert').append(inner);
new variable
const main = document.querySelector('div#main'); document.querySelector('div#insert').append(main.querySelector('div#inner'));

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
multiple querySelector
new variable

Fastest: N/A

Slowest: N/A

Latest 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 break down the provided benchmark and explain what's being tested, compared, and their pros and cons.

**Benchmark Overview**

The test case measures the performance difference between two approaches:

1. **multiple querySelector**: This approach uses `querySelector` twice to select an element and its inner element.
   ```javascript
const main = document.querySelector('div#main');
const inner = main.querySelector('div#inner');
document.querySelector('div#insert').append(inner);
```
2. **new variable**: This approach creates a new variable for the inner element selection, then appends it to another element.
   ```javascript
const main = document.querySelector('div#main');
document.querySelector('div#insert').append(main.querySelector('div#inner'));
```

**Comparison of Approaches**

Both approaches involve two `querySelector` calls. However, the first approach creates a new variable (`inner`) for the inner element selection, while the second approach uses a new variable for both selections.

**Pros and Cons:**

*   **multiple querySelector Approach**
    *   Pros:
        *   Can be beneficial when you need to reuse an intermediate result in your code.
        *   Some browsers may optimize this pattern.
    *   Cons:
        *   Results in two separate DOM queries, which can lead to slower performance due to additional work done by the browser engine.

*   **new variable Approach**
    *   Pros:
        *   Only results in one DOM query.
        *   This approach can be faster if you only need to append the inner element once.
    *   Cons:
        *   Creates an intermediate variable that consumes memory and might lead to garbage collection overhead.

**Library Usage**

The benchmark code uses JavaScript's built-in `document.querySelector` method, which is a part of the Document Object Model (DOM). This method allows you to navigate through the DOM tree by selecting elements based on their attributes, CSS selectors, or other criteria.

No third-party library is used in this benchmark. However, for reference, popular libraries like jQuery provide similar functionality with different syntax and features.

**Special JavaScript Features/Syntax**

The benchmark code uses a special feature of modern browsers: **Template Literals** (the backticks ``) are not necessary here. The example does not utilize any browser-specific features or modern JavaScript syntax (like async/await, ES6 classes, etc.).

Related benchmarks:

multiple querySelector vs new variable (version: 0)

double querySelector vs extra variable

Comparing performance of: multiple querySelector vs new variable

Created: 3 years ago by: Guest

Jump to the latest result

multiple querySelector

new variable

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):