Benchmark: Old MutationEvents performance 2

HTML Preparation code:

<div id="b"></div>

Script Preparation code:

function e() {}

function a(c) {
    c && document.addEventListener('DOMNodeInserted', e)
    for (let i = 100; i--;) {
        let element = b.cloneNode()
        document.body.appendChild(element)
        document.body.removeChild(element)
    }
    c && document.removeEventListener('DOMNodeInserted', e)
}

Tests:

Normal
a(false)
MutationEvents
a(true)

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Normal
MutationEvents

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one month ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:136.0) Gecko/20100101 Firefox/136.0

Browser/OS: Firefox 136 on Linux

View result in a separate tab

Test name	Executions per second
Normal	2535.5 Ops/sec
MutationEvents	1515.9 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):

LLMs can make mistakes. Check important info.

The provided benchmark tests the performance impact of using Mutation Events in JavaScript through two scenarios executed in a web environment. Specifically, the benchmarks test the behavior of the `addEventListener` and `removeEventListener` methods when adding and removing elements from the DOM.

### Explanation of the Benchmark

#### Benchmark Preparation Code
The benchmark prepares an environment to test the performance of DOM manipulation by using the following approach:

1. **Function Definition**: It defines two functions:
   - `e()`: An empty function meant to serve as a callback for event handling.
   - `a(c)`: A function that accepts a boolean `c`.
     - If `c` is true, it adds an event listener for the `DOMNodeInserted` event.
     - It then iterates 100 times, cloning a DOM element (represented by an empty `<div>` with `id="b"`) and appending it to the document's body, followed by removing it.
     - If `c` is true, it removes the event listener after the iterations.

#### Test Cases
Two distinct test cases are defined, each testing the same overall functionality but differing in how the event listener is handled:

1. **Normal (a(false))**: This test case disables the Mutation Event listener. The function `a(false)` runs the DOM manipulation without tracking the inserted nodes.

2. **MutationEvents (a(true))**: This test case enables the Mutation Event listener. The function `a(true)` runs the same DOM manipulation while tracking the insertion of nodes through the event listener.

### Performance Metrics
The benchmark results show the `ExecutionsPerSecond` for each test:

- **Normal (a(false))**: 2535.47 executions per second
- **MutationEvents (a(true))**: 1515.90 executions per second

### Pros and Cons of Approaches

#### Using Mutation Events (`MutationEvents`)
**Pros**:
- It allows developers to respond to changes in the DOM, making it suitable for scenarios where you need to trigger actions based on element insertion.
  
**Cons**:
- **Performance Overhead**: Keeping track of every modification to the DOM can lead to a significant performance hit. This is evident in the benchmark, where using Mutation Events reduces the execution speed to about 60% of the non-Mutation Events scenario.
- **Compatibility**: Different browsers may handle Mutation Events differently, leading to potential inconsistencies.

#### Not Using Mutation Events (`Normal`)
**Pros**:
- **Higher Performance**: The benchmark demonstrates faster execution due to the absence of overhead from event tracking.
- **Simplicity**: For many operations involving frequent DOM manipulation, using traditional methods may suffice, promoting better performance.

**Cons**:
- Loss of reactive capabilities: By not using event listeners, it is not possible to respond dynamically to changes in the DOM.

### Considerations and Alternatives

1. **MutationObserver API**: 
   - This modern API is an alternative to Mutation Events. It provides a more efficient way to respond to changes in the DOM without incurring the heavy performance costs associated with Mutation Events. It allows developers to observe changes asynchronously and potentially use batching to minimize layout recalculations.

2. **Performance Impact**: Understanding the performance implications is key in web development. While using listeners might seem fruitful for interactivity, benchmarks like this help highlight when to optimize code paths—especially in heavy DOM manipulation scenarios.

### Conclusion
The provided benchmarks illustrate a crucial trade-off in web development between functionality (using event listeners) and performance. Evaluating different JavaScript techniques, such as the older Mutation Events versus the modern MutationObserver or directly manipulating the DOM without reactive measures, remains essential for building efficient web applications.

Related benchmarks:

Old MutationEvents performance 2 (version: 1)

Comparing performance of: Normal vs MutationEvents

Created: one month ago by: Guest

Jump to the latest result

Normal

MutationEvents

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated one month ago):