Benchmark: startsWith vs str[0] === char

HTML Preparation code:

<div></div>

Script Preparation code:

window.regex = /^test/;
window.match = 'test';
var data = window.data = [];
const possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
var TOTAL_STRINGS = window.TOTAL_STRINGS = 100000;

function makeRandomString(len) {
  var text = "";
  for( var i=0; i < len; i++ ) {
    text += possible.charAt(0);
  }
  return text;
}

while (data.length < TOTAL_STRINGS) {
  data.push(makeRandomString(1));
}

Tests:

.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]; match.startsWith(str); x += 1; }
str[0]
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]; match[0] === str[0]; x += 1; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
.startsWith
str[0]

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/125.0.0.0 Safari/537.36

Browser/OS: Chrome 125 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
.startsWith	4527.7 Ops/sec
str[0]	5321.5 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the benchmark and its test cases.

**Benchmark Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided JSON represents a benchmark with two test cases: `startsWith` and `str[0]`. The goal of this benchmark is to compare the performance of these two approaches for checking if a string starts with a specific character.

**Benchmark Definition**

The benchmark definition provides some setup code that is executed before running each test case. This code:

* Defines a regular expression `window.regex = /^test/;` (not used in the benchmark)
* Sets up an array `window.data` to store random strings
* Initializes a string constant `possible` containing all ASCII characters (0-255) and `TOTAL_STRINGS` set to 100,000

The `makeRandomString(len)` function generates a random string of length `len` by concatenating the first character of `possible` for each iteration.

**Individual Test Cases**

There are two test cases:

### 1. `.startsWith`

This test case uses the `window.match.startsWith(str);` expression to check if the string `str` starts with a specific character.

* The benchmark definition assigns the values of `TOTAL_STRINGS`, `data`, and `match` to the local scope.
* The test loop iterates from `x = 0` to `TOTAL_STRINGS - 1`, pushing each random string into the `data` array.
* In each iteration, it calls `match.startsWith(str);` on the assigned value of `match`.

### 2. `str[0] === char`

This test case uses the expression `match[0] === str[0];` to check if the first character of `str` is equal to a specific character.

**Pros and Cons**

* **.startsWith**: This approach is generally faster because it uses a built-in method that is optimized for performance.
	+ Pros: Fast execution, good cache locality
	+ Cons: May be slower for large strings due to overhead of method call
* `str[0] === char`: This approach can be slower because it requires manual indexing and comparison.
	+ Pros: Simple and easy to understand, potentially faster for small strings
	+ Cons: Can be slower than `.startsWith` for larger strings

**Other Considerations**

* The use of a regular expression in the benchmark definition is unnecessary and can introduce overhead. It's likely that this line will be removed or commented out.
* The `makeRandomString(len)` function generates random strings by concatenating the first character of `possible`. This approach may not be suitable for large string lengths, as it can lead to performance issues due to excessive memory allocation.

**Alternatives**

If you wanted to write similar benchmarks using alternative approaches, here are some options:

* Use a different method for checking if a string starts with a specific character, such as `str.indexOf('char') > -1`.
* Use a library like Lodash or String.prototype to perform the comparison.
* Test different scenarios, such as searching for characters in a string using `str.indexOf('char')`.

Keep in mind that benchmarking is an art, and the best approach will depend on your specific use case and performance requirements.

Related benchmarks:

startsWith vs str[0] === char (version: 0)

Testing some things

Comparing performance of: .startsWith vs str[0]

Created: 4 years ago by: Guest

Jump to the latest result

.startsWith

str[0]

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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