Benchmark: Regex vs .indexOf vs .startsWith vs .substr

HTML Preparation code:

<div></div>

Script Preparation code:

window.regex = new RegExp("^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:

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

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Regex
.indexOf

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 4 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.106 Safari/537.36

Browser/OS: Chrome 83 on Windows

View result in a separate tab

Test name	Executions per second
Regex	381.6 Ops/sec
.indexOf	496.4 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll provide an explanation of the provided JSON, benchmark options, and considerations.

**Benchmark Definition JSON**

The `benchmark.json` file defines two test cases:

1. **`Regex`**: Tests the performance of using a regular expression (`regex`) to check if a string (`str`) matches a pattern.
2. **`.indexOf`**, **`.startsWith`**, and **`.substr`**: Tests the performance of using the `.indexOf`, `.startsWith`, and `.substr` methods, respectively, on strings.

**Options Compared**

The benchmark compares the performance of:

1. **Regular Expressions (`regex`)**: Using a regular expression to search for a pattern in a string.
2. **`.indexOf`**: Using the `.indexOf` method to find the index of a substring within another string.
3. **`.startsWith`**: Using the `.startsWith` method to check if a string starts with another string.
4. **`.substr`**: Using the `.substr` method to extract a subset of characters from a string.

**Pros and Cons**

*   **Regular Expressions (`regex`)**:
    *   Pros: flexible pattern matching, support for character classes, anchors, and quantifiers.
    *   Cons: slower performance due to the complexity of pattern matching.
*   **`.indexOf`**, **`.startsWith`**, and **`.substr`**:
    *   Pros: faster performance since they are optimized for simple substring searches.
    *   Cons: limited flexibility and support for complex patterns.

**Library Used**

None explicitly mentioned, but it's likely that the `RegExp` constructor is being used to create a regular expression object.

**Special JS Feature or Syntax**

No special JavaScript features or syntax are explicitly mentioned in this benchmark.

**Other Considerations**

*   **Data Generation**: The benchmark generates random strings using a predefined character set (`ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789`) to simulate real-world string data.
*   **Looping**: Both test cases use a `while` loop to iterate over the generated strings, ensuring that each string is processed multiple times.

**Alternative Benchmarks**

Other benchmarks could be used to compare these options:

1.  **`.includes`**: Using the `.includes` method instead of `.indexOf`.
2.  **String.prototype.match()**: Using the `match()` method instead of regular expressions.
3.  **Array.prototype.includes()**: Using the `includes()` method on arrays instead of strings.

These alternatives would provide additional insights into the performance characteristics of each option in different contexts.

Related benchmarks:

Regex vs .indexOf vs .startsWith vs .substr (version: 0)

Testing some things

Comparing performance of: Regex vs .indexOf

Created: 4 years ago by: Guest

Jump to the latest result

Regex

.indexOf

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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