Benchmark: JS Regex vs .startsWith vs .indexOf but with lowercase when checking index

HTML Preparation code:

<div></div>

Script Preparation code:

window.regexStart = /^test/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.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.toLowerCase().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.toLowerCase().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: one year ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/117.0.0.0 Safari/537.36

Browser/OS: Chrome 117 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
regex start	612.4 Ops/sec
startsWith	443.8 Ops/sec
indexOf start	12119.7 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript microbenchmarks!

**Benchmark Overview**

The provided benchmark is designed to compare the performance of three different string matching methods: regular expressions (regex), `startsWith`, and `indexOf` with a case-insensitive comparison using `.toLowerCase()`.

**Script Preparation Code**

Before running each test, the script prepares the following variables:

* `window.regexStart`: a regex pattern (`/^test/i`) that matches the string "test" in a case-insensitive manner.
* `window.match`: the target string to be matched ("test").
* `window.matchLength`: the length of the target string (1).
* `data`: an array of 100,000 random strings generated using a custom function `makeRandomString(len)`.
* `TOTAL_STRINGS`: the total number of strings in the `data` array.

**Individual Test Cases**

There are three test cases:

### regex start

This test case uses the `window.regexStart` pattern to match each string in the `data` array. The regex pattern is designed to be case-insensitive, but it's not explicitly specified in the benchmark definition.

Pros: Regular expressions can provide more flexibility and power when working with strings, including support for complex patterns, capturing groups, and Unicode characters.

Cons: Regular expressions can be slower than other methods due to their complexity and the overhead of compiling the pattern.

### startsWith

This test case uses the `startsWith` method to check if each string in the `data` array starts with the target string "test" (case-insensitive).

Pros: The `startsWith` method is a built-in method that can provide fast performance, as it only needs to compare a single character at a time.

Cons: This method may not work correctly for strings containing Unicode characters or non-ASCII characters.

### indexOf start

This test case uses the `indexOf` method with `.toLowerCase()` to find the index of each string in the `data` array that starts with "test" (case-insensitive).

Pros: The `indexOf` method can provide fast performance, as it only needs to iterate through the string until finding the target character.

Cons: This method may not work correctly for strings containing Unicode characters or non-ASCII characters.

**Library and Special Features**

The benchmark uses a custom JavaScript function `makeRandomString(len)` to generate random strings. There are no special features used in this benchmark that require explicit mention.

**Other Alternatives**

If you were to reimplement this benchmark, you could also consider using other string matching methods, such as:

* `includes`: a new method introduced in ECMAScript 2017 (ES2017) that checks if a string contains a specified value.
* `match`: another method that can be used with regex patterns to search for matches in a string.
* `replaceAll`: a method that replaces all occurrences of a specified pattern in a string.

Keep in mind that the performance of these methods may vary depending on the specific use case and requirements.

Related benchmarks:

JS Regex vs .startsWith vs .indexOf but with lowercase when checking index (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: one year ago by: Guest

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):