Benchmark: className.indexOf vs. className.startsWith

HTML Preparation code:

<div id="foo" class="test"></div>

Script Preparation code:

var element = document.getElementById("foo");

Tests:

className
element.className.indexOf("test")
classList
element.className.startsWith("test");

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
className
classList

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.

I'd be happy to explain the provided benchmark and its test cases.

**Overview of MeasureThat.net**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks, which are small tests designed to measure the performance of specific code snippets or functions. The website provides a platform for developers to compare different approaches to solving a problem and identify the most efficient solution.

**Benchmark Definition**

The benchmark definition provided on MeasureThat.net is as follows:
```json
{
    "Name": "className.indexOf vs. className.startsWith",
    "Description": null,
    "Script Preparation Code": "var element = document.getElementById(\"foo\");",
    "Html Preparation Code": "<div id=\"foo\" class=\"test\"></div>"
}
```
This benchmark definition consists of a script preparation code, which initializes an HTML element with the id `foo` and sets its class to `test`. The benchmark also includes two test cases: `className` and `classList`.

**Test Cases**

The two test cases are:

1. **`className`**: This test case measures the performance of the `indexOf` method on the `className` property of the HTML element.
```javascript
element.className.indexOf("test")
```
2. **`classList`**: This test case measures the performance of the `startsWith` method on the `classList` property of the HTML element, which is a new feature introduced in modern JavaScript (ECMAScript 2020).
```javascript
element.classList.startsWith("test")
```
**Comparison**

The two test cases compare the performance of using the `indexOf` method versus the `startsWith` method to check if the class name contains the substring `"test"`.

**Pros and Cons:**

1. **`indexOf` method**: This is a widely supported method that has been available since JavaScript 1.x. It returns the index of the first occurrence of the specified value, or -1 if not found.
	* Pros:
		+ Widely supported across browsers
		+ Fast and efficient implementation
	* Cons:
		+ Returns an integer index, which may not be as intuitive for certain use cases
2. **`startsWith` method**: This is a new feature introduced in ECMAScript 2020.
	* Pros:
		+ More intuitive interface than `indexOf`
		+ Returns a boolean value indicating whether the string starts with the specified prefix
	* Cons:
		+ Not supported by older browsers (e.g., Internet Explorer)
		+ May have slower performance compared to `indexOf` in some cases

**Library:**

The `classList` property is not a native JavaScript property, but rather an extension provided by modern browsers. The `startsWith` method on the `classList` property was introduced in ECMAScript 2020 as a standard feature.

**Special JS Feature or Syntax:**

Note that this benchmark does not use any special JavaScript features or syntax beyond what's available in ECMAScript 2020.

**Other Alternatives:**

If you need to implement string searching or substring matching without using the `indexOf` method, you may also consider using regular expressions. For example:
```javascript
element.className.match(/test/)
```
However, keep in mind that this approach can be slower than using `indexOf` and may have additional overhead due to regular expression parsing.

Overall, the benchmark provides a useful comparison of two different approaches to string searching in JavaScript, allowing developers to choose the most efficient solution for their specific use case.

Related benchmarks:

className.indexOf vs. className.startsWith (version: 0)

Comparing performance of: className vs classList

Created: 5 years ago by: Guest

Jump to the latest result

className

classList

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):