Benchmark: startsWith vs RegExp

Script Preparation code:

window.regexStart = /^test/;
window.regexEnd = /test$/;
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:

regexp
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; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
regexp
startsWith

Fastest: N/A

Slowest: N/A

Latest run results:

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, compared, and the pros and cons of different approaches.

**Benchmark Overview**

The benchmark compares two approaches for checking if a string starts with a given pattern: using `RegExp` (Regular Expressions) versus using the `startsWith()` method.

**Script Preparation Code**

The script preparation code sets up some global variables:

* `window.regexStart`: a RegExp object that matches any string starting with "test"
* `window.regexEnd`: not used in this benchmark, but likely intended to match any string ending with "test" (not relevant to the test)
* `window.match`: set to the string "test", which will be used as the pattern
* `window.matchLength`: stores the length of the `match` string
* `window.data`: an array of 100,000 random strings generated using the `makeRandomString()` function (explained below)
* `TOTAL_STRINGS`: sets the total number of strings in the `data` array

**makeRandomString() Function**

The `makeRandomString(len)` function generates a random string of length `len` by concatenating characters from a predefined alphabet (`possible`) using `Math.random()`.

**Individual Test Cases**

There are two test cases:

1. **RegExp**: uses the `regexStart.test(str)` expression to check if each string in `data` starts with "test"
2. **startsWith**: uses the `str.startsWith(match) === 0` expression to check if each string in `data` starts with "test"

**Comparison**

The benchmark compares the performance of these two approaches by executing each test case on a large dataset of random strings (`window.data`). The results are reported for each browser and device platform.

**Pros and Cons**

* **RegExp (startsWith is not used)**:
	+ Pros: can match more complex patterns using the `RegExp` syntax, provides more control over matching.
	+ Cons: slower than the `startsWith()` method due to the overhead of compiling a RegExp object, may perform unnecessary backtracking or flagging.
* **startsWith**:
	+ Pros: faster and more efficient than the `RegExp` approach, optimized for simple prefix matching.
	+ Cons: limited to exact prefix matching, less flexible than RegExp.

The use of `startsWith()` is generally considered more suitable when:

* The pattern is a fixed string
* The pattern is short (a few characters)
* Performance is critical

On the other hand, `RegExp` might be preferred when:

* The pattern is complex or requires regular expression features like quantifiers or anchors
* The need for precise control over matching outweighs performance considerations

Related benchmarks:

startsWith vs RegExp (version: 0)

Comparing performance of: regexp vs startsWith

Created: 4 years ago by: Guest

Jump to the latest result

regexp

startsWith

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):