alphanum.js

function alphanum(a, b) {
    
    const isdigit = ch => '0' <= ch  && ch <= '9';

    let min = Math.min(a.length, b.length);
    
    let i;
    for (i = 0; i < min; i++) {
        if (a.charCodeAt(i) !== b.charCodeAt(i)) break;
    }
    if (i === min) return a.length - b.length;
    
    if (isdigit(a[i])) {
        if (isdigit(b[i])) {
            if (a[i] === '0' || b[i] === '0') {
                let z;
                for (z = i - 1; z > 0; z--) {
                    if (a[z] !== '0') break;
                }
                if (!isdigit(a[z])) z++;
                if (a[z] === '0' || b[z] === '0') {
                    let j;
                    for (j = i; ; j++) {
                        if (b[j] !== '0') break;
                    }
                    for (;; i++) {
                        if (a[i] !== '0') break;
                    }
                    if (!isdigit(a[i])) {
                        if (isdigit(b[j])) {
                            return -1;
                        } else {
                            return i - j;
                        }
                    } else if (!isdigit(b[j])) {
                        return 1;
                    } else {
                        let cmp = a.charCodeAt(i) - b.charCodeAt(j);
                        for (i++, j++;; i++, j++) {
                            if (!isdigit(a[i])) {
                                if (isdigit(b[j])) {
                                    return -1;
                                } else {
                                    if (cmp) return cmp;
                                    return i - j;
                                }
                            } else if (!isdigit(b[j])) {
                                return 1;
                            }
                        }
                    }
                }
            }
            
            let cmp = a.charCodeAt(i) - b.charCodeAt(i);
            for (i++;; i++) {
                if (!isdigit(a[i])) {
                    if (isdigit(b[i])) {
                        return -1;
                    } else {
                        return cmp;
                    }
                } else if (!isdigit(b[i])) {
                    return 1;
                }
            }
        } else if (isdigit(a[i - 1])) {
            return 1;
        } else {
            return a.charCodeAt(i) - b.charCodeAt(i);
        }
    } else if (isdigit(b[i])) {
        if (isdigit(b[i - 1])) {
            return -1;
        } else {
            return a.charCodeAt(i) - b.charCodeAt(i);
        }
    } else {
        return a.charCodeAt(i) - b.charCodeAt(i);
    }
}