Perl's core::substr in JavaScript

How to use

You you can install via yarn add locutus and require this function via const substr = require('locutus/perl/core/substr').

It is important to use a bundler that supports tree-shaking so that you only ship the functions that you actually use to your browser, instead of all of Locutus, which is massive. Examples are: Parcel, webpack, or rollup.js. For server-side use this is typically less of a concern.

Examples

Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#	code	expected result
1	substr('hello', 0, 3)	'hel'
2	substr('hello', 1)	'ello'
3	substr('hello', -2)	'lo'

Notes

• Perl’s offset is 0-based, negative counts from end

Here's what our current JavaScript equivalent to Perl's core::substr looks like.

module.exports = function substr(str, offset, length) {
  //      discuss at: https://locutus.io/perl/substr/
  // parity verified: Perl 5.40
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Perl's offset is 0-based, negative counts from end
  //       example 1: substr('hello', 0, 3)
  //       returns 1: 'hel'
  //       example 2: substr('hello', 1)
  //       returns 2: 'ello'
  //       example 3: substr('hello', -2)
  //       returns 3: 'lo'

  str = String(str)
  const len = str.length

  // Handle negative offset (count from end)
  let start = offset < 0 ? len + offset : offset

  // Clamp start to valid range
  if (start < 0) {
    start = 0
  }
  if (start > len) {
    return ''
  }

  // If length is undefined, return rest of string
  if (length === undefined) {
    return str.substring(start)
  }

  // Handle negative length (leave that many chars at end)
  let end
  if (length < 0) {
    end = len + length
    if (end < start) {
      return ''
    }
  } else {
    end = start + length
  }

  return str.substring(start, end)
}

Think you can do better?

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we assimilate first iterations with imperfections, hoping for others to take issue with-and improve them. This unorthodox approach has worked very well to foster fun and fruitful collaboration, but please be reminded to use our creations at your own risk. THE SOFTWARE IS PROVIDED "AS IS" has never been more true than for Locutus.

Now go and: [ View on GitHub | Edit on GitHub | View Raw ]

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Ehm.. only 7 Perl functions?

We can use your help porting more. Have a rainy Sunday afternoon to spare and a taste for a porting puzzle?

• Get inspiration from the Perl documentation.
• Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

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