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

Script Preparation code:

var str = '!foo bar baz';
var noop = Function.prototype;

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();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
character index
charAt()
startsWith()
slice()

Fastest: N/A

Slowest: N/A

Latest run results:

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

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

**What is being tested?**

The benchmark tests four different methods to access the first character of a string in JavaScript:

1. **Character Index (`str[0]`)**: Directly accessing the first element of the string array using square brackets.
2. **`charAt()`**: Using the `charAt()` method to retrieve the first character of the string.
3. **`slice()`**: Using the `slice()` method with a starting index of 0 to retrieve the first character of the string.
4. **`startsWith()`**: Using the `startsWith()` method to check if the string starts with a specific character.

**Options compared**

The benchmark compares the performance of these four methods on the same input string.

**Pros and Cons of each approach:**

1. **Character Index (`str[0]`)**:
	* Pros: Simple, fast, and efficient.
	* Cons: May not work for non-ASCII characters or strings with Unicode code points > 255.
2. **`charAt()`**:
	* Pros: Well-documented, widely supported, and works with all types of strings.
	* Cons: May have a slight performance overhead due to the method call.
3. **`slice()`**:
	* Pros: Flexible, as it can be used to extract substrings or characters from any position in the string.
	* Cons: May require more computations than necessary for just accessing the first character.
4. **`startsWith()`**:
	* Pros: Simple and efficient for checking if a string starts with a specific character.
	* Cons: Not designed specifically for retrieving individual characters; may have performance overhead.

**Library usage**

None of these methods rely on external libraries.

**Special JS feature or syntax**

No special JavaScript features or syntax are used in these test cases. However, `startsWith()` was introduced in ECMAScript 2015 (ES6) and is supported by most modern browsers.

**Other alternatives**

If you need to access the first character of a string, but want to avoid using `charAt()` or the array index approach, you could consider:

1. **`String.prototype.at()`**: Introduced in ECMAScript 2022 (ES22), this method returns the Unicode code point at the specified position in the string.
2. **Regular expressions**: You can use regular expressions with the `match()` method to extract individual characters from a string.

Keep in mind that these alternatives may have different performance characteristics and are not directly comparable to the methods tested in the benchmark.

Related benchmarks:

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

Compare methods for testing string's beginning character.

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

Created: 5 years ago by: Guest

Jump to the latest result

character index

charAt()

startsWith()

slice()

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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