Benchmark: char index vs charAt() vs slice() vs startsWith() vs RegExp Fixed

Script Preparation code:

var str = '!foo bar baz';
var noop = Function.prototype;
var code = "!".charCodeAt(0)
var pattern = /^!/;

Tests:

character index
if (str[0] === '!') noop();
charAt()
if (str.charAt(0) === '!') noop();
startsWith()
if (str.startsWith('!')) noop();
slice()
if (str.slice(0, 1) === '!') noop();
RegExp
if (pattern.test(str)) noop();
charCodeAt
if(str.charCodeAt(0) === code) noop();
character index again
if (str[0] === '!') noop();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
character index
charAt()
startsWith()
slice()
RegExp
charCodeAt
character index again

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36

Browser/OS: Chrome 111 on Linux

View result in a separate tab

Test name	Executions per second
character index	9986010.0 Ops/sec
charAt()	9944444.0 Ops/sec
startsWith()	9912426.0 Ops/sec
slice()	9575970.0 Ops/sec
RegExp	5760889.0 Ops/sec
charCodeAt	6715545.0 Ops/sec
character index again	10095448.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the world of JavaScript benchmarks.

**What is being tested?**

The provided benchmark compares six different methods to check if the first character of a string is an exclamation mark (!). The methods being compared are:

1. Character index (`str[0]`)
2. `charAt()` method
3. `startsWith()` method
4. `slice()` method with a length of 1
5. Regular expression (`pattern.test(str)`)
6. `charCodeAt(0)` method

**Options and their pros and cons:**

1. **Character index (`str[0]`)**:
	* Pros: Fast, simple, and concise.
	* Cons: May not work correctly for Unicode characters or strings with leading whitespace.
2. **`charAt()` method**:
	* Pros: More explicit and readable than character indexing, works well with Unicode characters.
	* Cons: May be slower than character indexing due to the overhead of calling a function.
3. **`startsWith()` method**:
	* Pros: More concise and readable than slicing or indexing, works well with Unicode characters.
	* Cons: May be slower than slicing or indexing due to the overhead of calling a function.
4. **`slice()` method with length 1**:
	* Pros: Fast and simple, works well for both ASCII and Unicode characters.
	* Cons: May not work correctly if the string is empty.
5. **Regular expression (`pattern.test(str)`)**:
	* Pros: Highly flexible and powerful, can match complex patterns.
	* Cons: May be slower than other methods due to the overhead of compiling a regular expression.
6. **`charCodeAt(0)` method**:
	* Pros: Fast and simple, works well for ASCII characters.
	* Cons: May not work correctly for Unicode characters.

**Library usage**

The `RegExp` class is used in the benchmark, which is a built-in JavaScript library. It's used to create a regular expression pattern that matches an exclamation mark at the start of a string.

**Special JS feature or syntax**

There are no special features or syntaxes mentioned in the benchmark code. The focus is on comparing different methods for checking the first character of a string.

**Other alternatives**

If you need to optimize this kind of string check, consider the following:

* Use `String.prototype.match()`, which returns an array with the matched substring if it exists, or null otherwise.
* Use `String.prototype.indexOf()` and then check if the result is -1 (indicating no match).
* Use a more advanced regular expression engine like `es6-regex` for better performance.

Keep in mind that the best approach will depend on your specific use case, requirements, and performance constraints.

Related benchmarks:

char index vs charAt() vs slice() vs startsWith() vs RegExp Fixed (version: 0)

Compare methods for testing string's beggining character.

Comparing performance of: character index vs charAt() vs startsWith() vs slice() vs RegExp vs charCodeAt vs character index again

Created: one year ago by: Guest

Jump to the latest result

character index

charAt()

startsWith()

slice()

RegExp

charCodeAt

character index again

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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