locutus/esm/php/strings/strlen.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

import { ini_get } from "../info/ini_get.js";
export function strlen(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
    if (typeof string === 'undefined') {
        throw new Error('strlen() expects exactly 1 argument, 0 given');
    }
    const str = string + '';
    const iniVal = ini_get('unicode.semantics') || 'off';
    if (iniVal === 'off') {
        return str.length;
    }
    let i = 0;
    let lgth = 0;
    const getWholeChar = function (str, i) {
        const code = str.charCodeAt(i);
        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) {
                throw new Error('High surrogate without following low surrogate');
            }
            const next = str.charCodeAt(i + 1);
            if (next < 0xdc00 || next > 0xdfff) {
                throw new Error('High surrogate without following low surrogate');
            }
            return str.charAt(i) + str.charAt(i + 1);
        }
        else if (code >= 0xdc00 && code <= 0xdfff) {
            // Low surrogate
            if (i === 0) {
                throw new Error('Low surrogate without preceding high surrogate');
            }
            const prev = str.charCodeAt(i - 1);
            if (prev < 0xd800 || prev > 0xdbff) {
                // (could change last hex to 0xDB7F to treat high private surrogates
                // as single characters)
                throw new Error('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
            return false;
        }
        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;
}