index.js

'use strict'

var slice = Array.prototype.slice;

function getPluralNoun(num) {
    var forms = slice.call(arguments, 1);

    var str;

    switch (forms.length) {
        case 1:
            throw new Error('Not enough forms');
            break;

        case 2:
            str = num > 1 ? forms[1] : forms[0];
            break;

        default:
            str = forms[getNounPluralForm(num)];
            break;
    }

    return str.replace(/%d/g, num);
}

function getPluralVerb(num) {
    var forms = slice.call(arguments, 1);
    var str = forms[getVerbPluralForm(num)];

    return str.replace(/%d/g, num);
}

function getVerbPluralForm(a) {
    if (a > 1000000) {
        return 2;
    }

    if (a > 1000 && a < 1000000 && /000$/.test(a)) {
        a /= 1000;
    }

    if (a % 10 === 1 && a % 100 !== 11 || /1000$/.test((a).toString())) {
        return 0;
    } else if (a % 10 >= 2 && a % 10 <= 4 && (a % 100 < 10 || a % 100 >= 20)) {
        return 1;
    } else {
        return 2;
    }
}

function getNounPluralForm(a) {
    if (a % 10 === 1 && a % 100 !== 11) {
        return 0;
    } else if (a % 10 >= 2 && a % 10 <= 4 && (a % 100 < 10 || a % 100 >= 20)) {
        return 1;
    } else {
        return 2;
    }
}

module.exports = getPluralNoun;
module.exports.noun = getPluralNoun;
module.exports.verb = getPluralVerb;