Benchmark: JS Regex vs .startsWith vs .indexOf by Jarvis

HTML Preparation code:

<div></div>

Script Preparation code:

window.regexStart = /^not/;
window.match = 'not';
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.regexStart; 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) === 0; 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.indexOf(match) === 0; x += 1; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
regex start
startsWith
indexOf start

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0

Browser/OS: Firefox 88 on Windows

View result in a separate tab

Test name	Executions per second
regex start	183.5 Ops/sec
startsWith	217.8 Ops/sec
indexOf start	163.0 Ops/sec

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

LLMs can make mistakes. Check important info.

**Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks to compare the performance of different approaches on various platforms. The provided benchmark definition json represents a test case with three individual tests: "regex start", "startsWith", and "indexOf start". We'll break down what's tested, describe the options compared, pros and cons of each approach, and discuss other considerations.

**Tested Options**

1. **Regex Start**: This option uses the `test()` method of a regular expression object (`window.regexStart`) to check if a given string matches a certain pattern.
2. **startsWith**: This option uses the `startsWith()` method of a string object (`window.match`) to check if a string starts with a certain prefix.
3. **IndexOf Start**: This option uses the `indexOf()` method of a string object (`window.match`) to find the index of the first occurrence of a certain substring.

**Options Compared**

The three options are compared in terms of their performance (measured by executions per second) on a desktop platform with Firefox 88 browser.

**Pros and Cons**

* **Regex Start**:
	+ Pros: Can match any pattern, not limited to prefixes.
	+ Cons: Can be slower due to the complexity of regular expressions, especially for complex patterns.
* **startsWith**:
	+ Pros: Fast and efficient for prefix matching, as it only checks a few characters.
	+ Cons: Limited to checking prefixes only, may not match more complex patterns.
* **IndexOf Start**:
	+ Pros: Faster than Regex Start, but still slower than StartsWith due to the overhead of searching for the index.
	+ Cons: May be less efficient for prefix matching compared to StartsWith.

**Library and Special JS Features**

* The `window.regexStart` object uses a regular expression pattern (`/^not/`) that is not a standard JavaScript regex pattern. This suggests that MeasureThat.net might be testing the performance of custom regex patterns or patterns that are specific to the Firefox browser.
* The `window.match` object uses the `startsWith()` method, which was introduced in ECMAScript 2022 (ES12).

**Considerations**

* The benchmark definition json uses a fixed string length (`20`) for generating random strings, which might not be representative of real-world scenarios where string lengths can vary.
* The number of iterations (`TOTAL_STRINGS = 100000`) is relatively low compared to other benchmarks, which may affect the accuracy of the results.
* MeasureThat.net provides detailed information about the browser and platform used, which can help identify performance differences due to hardware or software factors.

**Alternative Approaches**

Other approaches for prefix matching could include:

* Using a simple substring comparison (e.g., `str.includes(match)` or `str.localeCompare(match)`)
* Using a library like `lodash` or `underscore`, which provide optimized implementations of prefix matching methods
* Using a different JavaScript engine or browser, to see if performance differences are due to specific implementation details.

Keep in mind that these alternative approaches may have different trade-offs in terms of complexity, performance, and accuracy.

Related benchmarks:

JS Regex vs .startsWith vs .indexOf by Jarvis (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

Created: 3 years ago by: Registered User

Jump to the latest result

regex start

startsWith

indexOf start

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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