JavaScript camelCase Conversion

"use strict";

//
// camelCase v6.0.0
//
// Convert a dash/dot/underscore/space separated string to camelCase or PascalCase: foo-bar > fooBar
// Correctly handles Unicode strings. Correctly handles Unicode strings.
//
// Author/License: Copyright (c) MIT Sindre Sorhus <sindresorhus@gmail.com> (https://sindresorhus.com)
// GitHub: https://github.com/sindresorhus/camelcase
//
// Usage:
//
// camelCase('foo-bar');
// //=> 'fooBar'
//
// camelCase('foo_bar');
// //=> 'fooBar'
//
// camelCase('Foo-Bar');
// //=> 'fooBar'
//
// camelCase('розовый_пушистый_единороги');
// //=> 'розовыйПушистыйЕдинороги'
//
// camelCase('Foo-Bar', {pascalCase: true});
// //=> 'FooBar'
//
// camelCase('--foo.bar', {pascalCase: false});
// //=> 'fooBar'
//
// camelCase('foo bar');
// //=> 'fooBar'
//
// console.log(process.argv[3]);
// //=> '--foo-bar'
// camelCase(process.argv[3]);
// //=> 'fooBar'
//
// camelCase(['foo', 'bar']);
// //=> 'fooBar'
//
// camelCase(['__foo__', '--bar'], {pascalCase: true});
// //=> 'FooBar'
//
// Author/License: Copyright (c) MIT Sindre Sorhus <sindresorhus@gmail.com> (https://sindresorhus.com)
// GitHub: https://github.com/sindresorhus/camelcase
//

var _preserveCamelCase = function (string) {
    var isLastCharLower = false;
    var isLastCharUpper = false;
    var isLastLastCharUpper = false;

    for (var i = 0; i < string.length; i++) {
        var character = string[i];
        if (
            isLastCharLower &&
            /[a-zA-Z]/.test(character) &&
            character.toUpperCase() === character
        ) {
            string = string.slice(0, i) + "-" + string.slice(i);
            isLastCharLower = false;
            isLastLastCharUpper = isLastCharUpper;
            isLastCharUpper = true;
            i++;
        } else if (
            isLastCharUpper &&
            isLastLastCharUpper &&
            /[a-zA-Z]/.test(character) &&
            character.toLowerCase() === character
        ) {
            string = string.slice(0, i - 1) + "-" + string.slice(i - 1);
            isLastLastCharUpper = isLastCharUpper;
            isLastCharUpper = false;
            isLastCharLower = true;
        } else {
            isLastCharLower =
                character.toLowerCase() === character &&
                character.toUpperCase() !== character;
            isLastLastCharUpper = isLastCharUpper;
            isLastCharUpper =
                character.toUpperCase() === character &&
                character.toLowerCase() !== character;
        }
    }

    return string;
};

var camelCase = function (input, options) {
    if (!(typeof input === "string" || Array.isArray(input))) {
        throw new TypeError("Expected the input to be `string | string[]`");
    }

    options = Object.assign({ pascalCase: false }, options);

    var postProcess = function (x) {
        return options.pascalCase ? x.charAt(0).toUpperCase() + x.slice(1) : x;
    };

    if (Array.isArray(input)) {
        input = input
            .map(function (x) {
                return x.trim();
            })
            .filter(function (x) {
                return x.length;
            })
            .join("-");
    } else {
        input = input.trim();
    }

    if (input.length === 0) {
        return "";
    }

    if (input.length === 1) {
        return options.pascalCase ? input.toUpperCase() : input.toLowerCase();
    }

    var hasUpperCase = input !== input.toLowerCase();
    if (hasUpperCase) {
        input = _preserveCamelCase(input);
    }

    input = input
        .replace(/^[_.\- ]+/, "")
        .toLowerCase()
        .replace(/[_.\- ]+(\w|$)/g, function (_, p1) {
            return p1.toUpperCase();
        })
        .replace(/\d+(\w|$)/g, function (m) {
            return m.toUpperCase();
        });

    return postProcess(input);
};