Benchmark: JS Regex vs .startsWith vs .indexOf Jan

HTML Preparation code:

<div></div>

Script Preparation code:

window.regexpStart = new RegExp('^p.*', 'i');
window.match = 'test';
window.matchLength = window.match.length;
var data = window.data = [];
const possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
var TOTAL_STRINGS = window.TOTAL_STRINGS = 100000;

function getRandomInt(max) {
  return Math.floor(Math.random() * max);
}

function makeRandomString(len) {
  var text = "";
  for( var i=0; i < len; i++ ) {
    text += possible.charAt(getRandomInt(possible.length));
  }
  return text;
}

while (data.length < TOTAL_STRINGS) {
  data.push(makeRandomString(getRandomInt(20)));
}

Tests:

regex start
var x = 0; var TOTAL_STRINGS = window.TOTAL_STRINGS; var data = window.data; var regex = window.regexpStart; while (x < TOTAL_STRINGS) { const str = data[x]; regex.test(str); x += 1; }
startsWith
var x = 0; var TOTAL_STRINGS = window.TOTAL_STRINGS; var data = window.data; var match = window.match; while (x < TOTAL_STRINGS) { const str = data[x]; str.startsWith(match); x += 1; }
indexOf start
var x = 0; var TOTAL_STRINGS = window.TOTAL_STRINGS; var data = window.data; var match = window.match; while (x < TOTAL_STRINGS) { const str = data[x]; str.toLowerCase().indexOf(match) === 0; x += 1; }
toLowerCase().startsWith
var x = 0; var TOTAL_STRINGS = window.TOTAL_STRINGS; var data = window.data; var match = window.match; while (x < TOTAL_STRINGS) { const str = data[x]; str.toLowerCase().startsWith(match); x += 1; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
regex start
startsWith
indexOf start
toLowerCase().startsWith

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 29 days ago):

LLMs can make mistakes. Check important info.

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

**Overview**

The provided benchmark measures the performance of three different methods to check if a string starts with a given pattern: `regex.start`, `startsWith`, and `toLowerCase().startsWith`. The benchmark generates 100,000 random strings and checks each one against the patterns using a while loop. The results are compared across different browsers and devices.

**Options being compared**

1. **Regex (`regex.start`)**: This method uses a regular expression to check if the string starts with the given pattern.
2. **`startsWith`**: This method directly checks if the string starts with the given substring using the `startsWith` method of JavaScript strings.
3. **`toLowerCase().startsWith`**: This method first converts the string to lowercase and then checks if it starts with the given substring using `startsWith`.

**Pros and Cons**

1. **Regex (`regex.start`)**:
	* Pros: Regular expressions are powerful pattern-matching tools that can handle complex patterns, including negations, repetitions, and character classes.
	* Cons: Regular expressions can be slow due to their complexity and the need to compile them before use. They also have a steeper learning curve than other methods.
2. **`startsWith`**:
	* Pros: This method is simple and efficient, as it only requires a single operation to compare the string against the substring.
	* Cons: This method may not be suitable for complex pattern matching or when working with non-ASCII characters, where the `startsWith` method may return incorrect results due to Unicode normalization issues.
3. **`toLowerCase().startsWith`**:
	* Pros: This method is efficient and can handle both ASCII and non-ASCII strings, as it converts the string to lowercase before comparison.
	* Cons: This method requires an additional operation (converting to lowercase) and may not be suitable for complex pattern matching.

**Library usage**

There are no explicit libraries used in this benchmark. However, the `RegExp` constructor is used to create a regular expression object, which is then used to check if the string starts with the given pattern.

**Special JavaScript features or syntax**

None of the methods use any special JavaScript features or syntax beyond what's standard for JavaScript strings and regular expressions.

**Alternative approaches**

If you're interested in exploring alternative approaches, here are some other options:

1. **Use a dedicated string matching library**: Libraries like `string-matching` (Node.js) or `substr` (Browser-based) provide optimized string matching algorithms that might outperform the built-in methods used in this benchmark.
2. **Implement a custom string matching algorithm**: You could implement your own string matching algorithm using techniques like Boyer-Moore or Knuth-Morris-Pratt, which can be more efficient than the built-in methods for specific use cases.

In summary, the choice of method depends on your specific requirements and constraints. If you need to match complex patterns or work with non-ASCII strings, regular expressions might be a good choice. For simple string matching, `startsWith` is likely to be sufficient. Converting to lowercase before comparison can provide a good balance between simplicity and efficiency.

Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.82 Safari/537.36

Browser/OS: Chrome 93 on Windows

View result in a separate tab

Test name	Executions per second
regex start	531.4 Ops/sec
startsWith	634.8 Ops/sec
indexOf start	10898.2 Ops/sec
toLowerCase().startsWith	326.5 Ops/sec

Related benchmarks:

JS Regex vs .startsWith vs .indexOf Jan (version: 0)

fork of https://www.measurethat.net/Benchmarks/Show/975/11/regex-vs-indexof-vs-startswith-vs-substr

Comparing performance of: regex start vs startsWith vs indexOf start vs toLowerCase().startsWith

Created: 3 years ago by: Guest

Jump to the latest result

regex start

startsWith

indexOf start

toLowerCase().startsWith

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 29 days ago):