pluralizer.js

const wordPlural = (word, amount) => {
    word = word.toLowerCase()
    if (amount === 1) {
        return word
    }

    return pluralize(word)
}

const pluralize = word => {
    return getPluralRule(word)
        .pluralize(word)
}

const getPluralRule = word => {
    const exceptions = {
        roof: 'roofs',
        belief: 'beliefs',
        chef: 'chefs',
        chief: 'chiefs',
        gas: 'gasses',
        fez: 'fezzes',
        man: 'men',
        woman: 'women',
        child: 'children',
        goose: 'geese',
        tooth: 'teeth'
    }

    if (exceptions[word]) {
        return { pluralize: word => exceptions[word] }
    }

    const rules = [
        { matcher: '(sh|s+|ch|x|z)$', pluralize: word => `${word}es` },
        { matcher: '(f|fe)$', pluralize: word => word.replace(/(f|fe)$/, 'ves') },
        { matcher: '[^aeiou]y$', pluralize: word => word.replace(/y$/, 'ies') },
        { matcher: '[aeiou]y$', pluralize: word => `${word}s` },
        { matcher: 'o$', pluralize: word => `${word}es` },
        { matcher: '[a-z]+$', pluralize: word => `${word}s` }
    ]
    return rules
        .find(p => new RegExp(p.matcher).test(word))
}

const main = () => {
    const words = [
        'car', 'goose', 'banana', 'roof', 'belief',
        'elf', 'knife', 'gas', 'watch', 'batch',
        'bus', 'tooth', 'truss', 'lunch', 'wolf',
        'rubber', 'computer', 'headset', 'tomato', 'potato',
        'shrimp', 'man', 'clock', 'hand', 'wall',
        'room', 'mind', 'calling', 'breath', 'life']

    const logger = (word, i) => {
        if (i === 0) {
            console.log('iteration ==> singular ==> plural')
        }
        console.log(`${(i + 1).toString().padStart(2, '0').padEnd(9, ' ')} ==> ${wordPlural(word, 1).padEnd(8, ' ')} ==> ${wordPlural(word, 2)}`)
    }

    words.forEach(logger)
}


main()

thank you for your effort