PHP's substr in JavaScript

How to use

You you can install via yarn add locutus and require this function via const substr = require('locutus/php/strings/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('abcdef', 0, -1)	'abcde'
2	substr(2, 0, -6)	false
3	ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', 0, -1)	'a'
4	ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', 0, 2)	'a\uD801\uDC00'
5	ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', -1, 1)	'\uD801\uDC00'
6	ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00z\uD801\uDC00', -3, 2)	'\uD801\uDC00z'
7	ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00z\uD801\uDC00', -3, -1)	'\uD801\uDC00z'

Notes

• Handles rare Unicode characters if ‘unicode.semantics’ ini (PHP6) is set to ‘on’

Here’s what our current JavaScript equivalent to PHP's substr looks like.

module.exports = function substr(input, start, len) {
  //  discuss at: https://locutus.io/php/substr/
  // original by: Martijn Wieringa
  // bugfixed by: T.Wild
  // improved by: Onno Marsman (https://twitter.com/onnomarsman)
  // improved by: Brett Zamir (https://brett-zamir.me)
  //  revised by: Theriault (https://github.com/Theriault)
  //  revised by: Rafał Kukawski
  //      note 1: Handles rare Unicode characters if 'unicode.semantics' ini (PHP6) is set to 'on'
  //   example 1: substr('abcdef', 0, -1)
  //   returns 1: 'abcde'
  //   example 2: substr(2, 0, -6)
  //   returns 2: false
  //   example 3: ini_set('unicode.semantics', 'on')
  //   example 3: substr('a\uD801\uDC00', 0, -1)
  //   returns 3: 'a'
  //   example 4: ini_set('unicode.semantics', 'on')
  //   example 4: substr('a\uD801\uDC00', 0, 2)
  //   returns 4: 'a\uD801\uDC00'
  //   example 5: ini_set('unicode.semantics', 'on')
  //   example 5: substr('a\uD801\uDC00', -1, 1)
  //   returns 5: '\uD801\uDC00'
  //   example 6: ini_set('unicode.semantics', 'on')
  //   example 6: substr('a\uD801\uDC00z\uD801\uDC00', -3, 2)
  //   returns 6: '\uD801\uDC00z'
  //   example 7: ini_set('unicode.semantics', 'on')
  //   example 7: substr('a\uD801\uDC00z\uD801\uDC00', -3, -1)
  //   returns 7: '\uD801\uDC00z'
  //        test: skip-3 skip-4 skip-5 skip-6 skip-7

  const _php_cast_string = require('../_helpers/_phpCastString') // eslint-disable-line camelcase

  input = _php_cast_string(input)

  const ini_get = require('../info/ini_get') // eslint-disable-line camelcase
  const multibyte = ini_get('unicode.semantics') === 'on'

  if (multibyte) {
    input = input.match(/[\uD800-\uDBFF][\uDC00-\uDFFF]|[\s\S]/g) || []
  }

  const inputLength = input.length
  let end = inputLength

  if (start < 0) {
    start += end
  }

  if (typeof len !== 'undefined') {
    if (len < 0) {
      end = len + end
    } else {
      end = len + start
    }
  }

  if (start > inputLength || start < 0 || start > end) {
    return false
  }

  if (multibyte) {
    return input.slice(start, end).join('')
  }

  return input.slice(start, end)
}

A community effort

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.

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