Benchmark: leftpad - MeasureThat.net

Script Preparation code:

function leftpad (str, len, ch) {
  str = String(str);
  var i = -1;
  if (!ch && ch !== 0) ch = ' ';
  len = len - str.length;
  while (++i < len) {
    str = ch + str;
  }
  return str;
}

function fastleftPad(value, size, pad) {
  if (value.length < size) {
    size -= value.length;
    var res = '';
    for(;;) {
      if (size & 1) res += pad;
        size >>= 1;
        if (size) pad += pad;
          else break;
    }
    return res + value;
  }
  return value;
}

function myleftpad (str, len, ch) {
  len=len-str.length;
  str+=ch.repeat(len);
  return str;
}

Tests:

leftpad
leftpad('anim',20,'0')
fastleftpad
fastleftPad('anim',20,'0')
mine
myleftpad('anim',20,'0')

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
leftpad
fastleftpad
mine

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Android 10; Mobile; rv:132.0) Gecko/132.0 Firefox/132.0

Browser/OS: Firefox Mobile 132 on Android

View result in a separate tab

Test name	Executions per second
leftpad	592859.2 Ops/sec
fastleftpad	2043461.0 Ops/sec
mine	2332544.5 Ops/sec

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

LLMs can make mistakes. Check important info.

I'd be happy to help you understand the benchmark and its results.

**Benchmark Overview**

The provided JSON represents two benchmark definitions:

1. `leftpad`: A function that takes three arguments - `str`, `len`, and `ch`. It creates a new string by repeating the character `ch` a specified number of times, until the total length reaches `len`.
2. `fastleftPad`: Another implementation of the same functionality as `leftpad`, but optimized for performance.
3. `myleftpad`: A third implementation that uses the `repeat()` method to create a new string.

**Options Compared**

The benchmark compares the execution times of these three implementations:

* `leftpad`
* `fastleftPad`
* `myleftpad`

These two functions (`fastleftPad` and `myleftpad`) are alternative approaches to solving the same problem. The main difference between them lies in their performance and code structure.

**Pros and Cons**

Here's a brief overview of each implementation:

1. **`leftpad`**:
	* Simple and easy to understand.
	* Uses string concatenation, which can be slow for large strings.
	* Not optimized for performance.
2. **`fastleftPad`**:
	* Optimized for performance by using bitwise operations to calculate the number of pads needed.
	* Still uses string concatenation, but with a more efficient loop.
	* Easier to read and understand than `myleftpad`.
3. **`myleftpad`**:
	* Uses the `repeat()` method, which is faster than string concatenation for large strings.
	* More concise and elegant code structure.
	* May be less readable due to its brevity.

**Library**

None of these implementations uses a library or external dependency.

**Special JavaScript Features/Syntax**

No special JavaScript features or syntax are used in these implementations. The use of `repeat()` is a standard feature introduced in ECMAScript 2015 (ES6).

**Other Considerations**

When choosing an implementation, consider the following factors:

* Performance: If you need to optimize for execution time, `fastleftPad` might be the best choice.
* Code readability and maintainability: `myleftpad` is a good option if you prioritize concise code over performance.
* Browser support: All three implementations should work in modern browsers.

**Alternatives**

If you don't like these implementations or want to explore other options, consider:

* Using a string padding library or utility function.
* Implementing the padding logic using a different data structure, such as an array or buffer.
* Using a just-in-time (JIT) compiler or optimizer to generate efficient code for the specific use case.

Keep in mind that these alternatives might not be directly comparable to the provided benchmark implementations.

Related benchmarks:

leftpad (version: 42)

blah

Comparing performance of: leftpad vs fastleftpad vs mine

Created: 9 years ago by: Registered User

Jump to the latest result

leftpad

fastleftpad

mine

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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