PHP's strlen in JavaScript

module.exports = functionstrlen (string) {
//  discuss at: https://locutus.io/php/strlen/
// original by: Kevin van Zonneveld (https://kvz.io)
// improved by: Sakimori
// improved by: Kevin van Zonneveld (https://kvz.io)
//    input by: Kirk Strobeck
// bugfixed by: Onno Marsman (https://twitter.com/onnomarsman)
//  revised by: Brett Zamir (https://brett-zamir.me)
//      note 1: May look like overkill, but in order to be truly faithful to handling all Unicode
//      note 1: characters and to this function in PHP which does not count the number of bytes
//      note 1: but counts the number of characters, something like this is really necessary.
//   example 1: strlen('Kevin van Zonneveld')
//   returns 1: 19
//   example 2: ini_set('unicode.semantics', 'on')
//   example 2: strlen('A\ud87e\udc04Z')
//   returns 2: 3
const str = string + ''
const iniVal = (typeofrequire !== 'undefined' ? require('../info/ini_get')('unicode.semantics') : undefined) || 'off'
if (iniVal === 'off') {
return str.length
  }
let i = 0
let lgth = 0
const getWholeChar = function (str, i) {
const code = str.charCodeAt(i)
let next = ''
let prev = ''
if (code >= 0xD800 && code <= 0xDBFF) {
// High surrogate (could change last hex to 0xDB7F to
// treat high private surrogates as single characters)
if (str.length <= (i + 1)) {
thrownewError('High surrogate without following low surrogate')
      }
      next = str.charCodeAt(i + 1)
if (next < 0xDC00 || next > 0xDFFF) {
thrownewError('High surrogate without following low surrogate')
      }
return str.charAt(i) + str.charAt(i + 1)
    } elseif (code >= 0xDC00 && code <= 0xDFFF) {
// Low surrogate
if (i === 0) {
thrownewError('Low surrogate without preceding high surrogate')
      }
      prev = str.charCodeAt(i - 1)
if (prev < 0xD800 || prev > 0xDBFF) {
// (could change last hex to 0xDB7F to treat high private surrogates
// as single characters)
thrownewError('Low surrogate without preceding high surrogate')
      }
// We can pass over low surrogates now as the second
// component in a pair which we have already processed
returnfalse
    }
return str.charAt(i)
  }
for (i = 0, lgth = 0; i < str.length; i++) {
if ((getWholeChar(str, i)) === false) {
continue
    }
// Adapt this line at the top of any loop, passing in the whole string and
// the current iteration and returning a variable to represent the individual character;
// purpose is to treat the first part of a surrogate pair as the whole character and then
// ignore the second part
    lgth++
  }
return lgth
}