Benchmark: substr vs repeat

Script Preparation code:

const x20k = 'x'.repeat( 20000 );

Tests:

substr
const xx = x20k.substr(0, 19921);
repeat
const yy = 'x'.repeat(19921);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
substr
repeat

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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I'd be happy to explain what's being tested in the provided benchmark.

**Benchmark Overview**

The benchmark compares two approaches to create a string of 20,000 repetitions of the character 'x'. The script preparation code creates a constant `x20k` containing this repeated string. Then, there are two test cases:

1. **substr**: Extract a substring from `x20k` with a length of 19,921 characters.
2. **repeat**: Create a new string by repeating the character 'x' 19,921 times directly.

**Comparison Options**

The benchmark is comparing two approaches to achieve the same result:

1. **Substring Extraction (substr)**: Using the `substr()` method to extract a substring from `x20k`.
2. **String Repetition (repeat)**: Creating a new string by repeating the character 'x' directly.

**Pros and Cons**

Here's a brief overview of each approach:

* **Substring Extraction (substr)**:
	+ Pros: Can be more efficient if you only need to extract a specific substring from an existing string.
	+ Cons: May incur additional overhead due to string slicing, which can create new objects in memory.
* **String Repetition (repeat)**:
	+ Pros: Creates a new string object without modifying the original `x20k` string.
	+ Cons: Can be less efficient if you're only repeating a small number of characters.

**Library and Special JS Features**

There is no explicit library being used in this benchmark. However, the use of the `repeat()` method is a special JavaScript feature that creates a new string by repeating a specified value (in this case, the character 'x') a specified number of times.

**Other Alternatives**

If you need to repeat a string multiple times, other alternatives could include:

* Using the `String.prototype.repeat()` method in modern browsers (introduced in ECMAScript 2015).
* Creating an array of the repeated characters and joining them using `Array.prototype.join()`.
* Implementing your own loop-based solution.

Keep in mind that these alternatives might have slightly different performance characteristics depending on the browser, engine, or specific use case.

Related benchmarks:

substr vs repeat (version: 0)

Comparing performance of: substr vs repeat

Created: 8 years ago by: Guest

Jump to the latest result

substr

repeat

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):