Benchmark: .indexOf vs .startsWith

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 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:

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

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 9 days ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/143.0.0.0 Safari/537.36 SberBrowser/35.0.0.0

Browser/OS: Chrome 143 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
.startsWith	159.2 Ops/sec
.indexOf	136.9 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Overview**

MeasureThat.net is a website that allows users to create and run JavaScript microbenchmarks. The provided benchmark tests two different string manipulation methods: `String.prototype.startsWith()` and `String.prototype.indexOf()`. We'll break down what's being tested, the options compared, pros and cons of each approach, and other considerations.

**Benchmark Definition JSON**

The benchmark definition JSON represents a script that sets up the environment for the test. It defines:

1. Variables:
	* `window.regex`: a regular expression object set to `/^test/`.
	* `window.match`: a string variable set to `"test"`.
	* `window.data`: an array of strings, initialized with 100,000 random strings.
	* `TOTAL_STRINGS`: a constant set to the length of the `window.data` array.
2. Functions:
	* `getRandomInt(max)`: generates a random integer between 0 and `max`.
	* `makeRandomString(len)`: generates a random string of length `len`.

**Individual Test Cases**

There are two test cases:

1. `.startsWith`
2. `.indexOf`

Each test case has a benchmark definition JSON that defines the script to be executed.

**Test Case: .startsWith**

The script checks each string in the `window.data` array using the `startsWith()` method and verifies that it returns true for the expected input `"test"`. The test case uses the `window.match` variable as the expected value.

**Pros and Cons of .startsWith()**

* **Pros:**
	+ Efficient, since it can stop searching as soon as it finds a match.
	+ Fewer comparisons required compared to `.indexOf()`.
* **Cons:**
	+ May be slower for large strings due to the overhead of string comparison.

**Test Case: .indexOf**

The script checks each string in the `window.data` array using the `.indexOf()` method and verifies that it returns 0 when searching for the expected input `"test"`. The test case uses the `window.match` variable as the expected value.

**Pros and Cons of .indexOf()**

* **Pros:**
	+ Can be faster than `.startsWith()` for large strings since it can return early.
* **Cons:**
	+ May require more comparisons to find the exact index, which can be slower.

**Library Use**

The benchmark uses the `window.match` variable, which is set to a string value `"test"`. This suggests that the library being tested is the `String.prototype.startsWith()` method. The purpose of this library is to check if a string starts with a specified substring.

**Special JS Features or Syntax**

None are explicitly mentioned in the benchmark code.

**Other Alternatives**

If you need to implement your own string manipulation methods, here are some alternatives:

* For checking if a string starts with a substring: use a loop that iterates over each character of the string.
* For checking if a string contains a specific substring: use a loop that searches for the substring within the string.

Keep in mind that these implementations will likely be slower and less efficient than using built-in methods like `.startsWith()` or `.indexOf()`.

Related benchmarks:

.indexOf vs .startsWith (version: 0)

Testing some things

Comparing performance of: .startsWith vs .indexOf

Created: 7 years ago by: Guest

Jump to the latest result

.startsWith

.indexOf

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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