PHP's substr in JavaScript

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

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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

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

input = _php_cast_string(input)

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

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

var inputLength = input.length
var 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)
}
[ View on GitHub | Edit on GitHub | Source on GitHub ]

How to use

You you can install via npm install locutus and require it via require('locutus/php/strings/substr'). You could also require the strings module in full so that you could access strings.substr instead.

If you intend to target the browser, you can then use a module bundler such as Browserify, webpack or rollup.js.

ES5/ES6

This function targets ES5, but as of Locutus 2.0.2 we also support ES6 functions. Locutus transpiles to ES5 before publishing to npm.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.

Notes

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

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.

#codeexpected result
1substr('abcdef', 0, -1)'abcde'
2substr(2, 0, -6)false
3ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', 0, -1)'a'
4ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', 0, 2)'a\uD801\uDC00'
5ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00', -1, 1)'\uD801\uDC00'
6ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00z\uD801\uDC00', -3, 2)'\uD801\uDC00z'
7ini_set('unicode.semantics', 'on') substr('a\uD801\uDC00z\uD801\uDC00', -3, -1)'\uD801\uDC00z'

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