node-slug.js

const { reduce } = require('lodash');

const replaceMap = {
    'a': '[àáâãäå]',
    'b': '[ß]',
    'c': '[ç]',
    'e': '[èéêë]',
    'i': '[ìíîï]',
    'o': '[ðñòóôõöø]',
    's': '[$]',
    'u': '[ùúû]',
    'y': '[ýýÿ]',
    '-': '([^a-z0-9]+|[-]{2,})'
};

module.exports = (str) => reduce(replaceMap, (result, pattern, letter) => {
    const regex = new RegExp(pattern, 'gi');
    return result.replace(regex, letter);
}, str);