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

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:

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.indexOf(match) === 0; 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) === true; x += 1; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Regex
.indexOf
.startsWith

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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Autogenerated LLM Summary (model gemma2:9b, generated one year ago):

LLMs can make mistakes. Check important info.

This benchmark tests the performance of three different methods for checking if a string starts with a specific substring:

* **Regex:** This method uses a regular expression (`/^test/`) to match the beginning of each string in the dataset.

* **`.indexOf`:** This method uses the `indexOf()` function to check if the target substring (`'test'`) is at index 0 within each string.

* **`.startsWith`:** This method directly utilizes the built-in `startsWith()` function to determine if a string starts with the specified substring (`'test'`).

**Pros and Cons:**

* **Regex:** 
    * **Pro:**  Highly flexible for complex patterns, can be optimized using flags.
    * **Con:** Can be slower than simpler methods due to its nature of parsing and matching against a pattern.

* **`.indexOf`:**
    * **Pro:** Relatively simple and straightforward implementation.
    * **Con:** Less performant than `.startsWith` in modern JavaScript engines.

* **`.startsWith`:** 
    * **Pro:**  Specifically designed for this task, often the most efficient option in recent browsers.
    * **Con:** Less flexible compared to regex if you need complex pattern matching.

**Alternatives:**

While these are common approaches, there might be other scenarios where a different method could be more suitable:

* **For very specific cases with known string patterns:**  Manually crafted string comparisons or bitwise operations could be surprisingly efficient.
* **If the target substring is frequently used:** Pre-checking and storing results in a lookup table can provide significant performance gains.

**Important Notes:** 
The benchmark results provided will vary depending on factors like browser, JavaScript engine version, and hardware. They offer a general idea of relative performance but should not be considered definitive for all situations.

Related benchmarks:

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

Testing some things

Comparing performance of: Regex vs .indexOf vs .startsWith

Created: 8 years ago by: Guest

Jump to the latest result

Regex

.indexOf

.startsWith

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model gemma2:9b, generated one year ago):