Benchmark: getElementById vs querySelector (class vs id)

HTML Preparation code:

<div id="t" class="t"></div>

Tests:

getElementById
var el = document.getElementById('t'); var className = el.className;
querySelector
var el = document.querySelector('.t'); var className = el.className;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
getElementById
querySelector

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 11 months ago)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:139.0) Gecko/20100101 Firefox/139.0

Browser/OS: Firefox 139 on Linux

View result in a separate tab

Test name	Executions per second
getElementById	4748257.0 Ops/sec
querySelector	3526863.5 Ops/sec

Autogenerated LLM Summary (model gpt-4o-mini, generated 11 months ago):

LLMs can make mistakes. Check important info.

The benchmark defined in the JSON evaluates the performance of two methods for selecting DOM elements in JavaScript: `getElementById` and `querySelector`.

### Options Compared

1. **getElementById**:
   - **Benchmark Definition**: 
     ```javascript
     var el = document.getElementById('t');
     var className = el.className;
     ```
   - **Test Name**: "getElementById"
   - **Purpose**: This method selects a single element based on its unique ID. In this case, it retrieves the `<div>` element with the ID "t".

2. **querySelector**:
   - **Benchmark Definition**: 
     ```javascript
     var el = document.querySelector('.t');
     var className = el.className;
     ```
   - **Test Name**: "querySelector"
   - **Purpose**: This method selects the first element that matches a specified CSS selector. Here, it retrieves the same `<div>` element by its class name "t".

### Performance Results

From the benchmark results, we see:
- **getElementById** achieved **17,275,460 executions per second**.
- **querySelector** achieved **13,366,061 executions per second**.

### Pros and Cons of Each Approach

#### getElementById

**Pros**:
- **Performance**: Generally faster than `querySelector` since it directly accesses elements by their ID, which is a unique identifier.
- **Simplicity**: Clear and straightforward when dealing with elements that have IDs.

**Cons**:
- Limited to selecting elements by their ID only; cannot handle complex queries.

#### querySelector

**Pros**:
- **Flexibility**: Can select elements using CSS selectors, allowing for complex selections (e.g., selecting by class, attribute, or even nested selections).
- **Consistency**: Works similarly to other CSS-based queries, making it easier for developers familiar with CSS to utilize.

**Cons**:
- **Performance**: Generally slower than `getElementById` for simple selections due to the overhead of parsing selectors and possibly querying multiple elements.
- **Potentially less efficient** in larger DOM trees or when used repeatedly in performance-critical situations.

### Libraries and Other Considerations

In this benchmark, there are no specific libraries tested; both methods are built-in JavaScript functionalities of the DOM API.

### Alternatives

- **getElementsByClassName**: Used to select elements by their class name. It returns a live HTMLCollection of elements, which can be beneficial or detrimental depending on the use case.
- **querySelectorAll**: Similar to `querySelector`, but returns a NodeList of all matching elements, not just the first one. This allows for more complex selections but has similar performance concerns.

### Conclusion

When choosing between `getElementById` and `querySelector`, developers should consider both performance and use case. If performance is critical and selection by ID is sufficient, `getElementById` is preferable. However, `querySelector` offers greater flexibility, allowing for more complex queries, which can be beneficial in many situations. Understanding these differences helps software engineers make informed decisions in their code.

Related benchmarks:

getElementById vs querySelector (class vs id) (version: 1)

Comparing performance of: getElementById vs querySelector

Created: 11 months ago by: Guest

Jump to the latest result

getElementById

querySelector

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model gpt-4o-mini, generated 11 months ago):