const findUndefinedness = require('find-undefinedness');

const config = {
    token: undefined,
    username: 'brh55',
    emoji: undefined
}
findUndefinedness(config);
//=> '[ 'token', 'emoji']

const findUndefinedness = require('find-undefinedness');

const user = {
    name: undefined,
    github: {
        username: 'brh55',
        repositories: {
            personal: 43,
            private: undefined
        },
        followers: {
            username: 'rightlag',
            repositories: {
                personal: 20,
                private: undefined
            },
            stars: 1
        },
        stars: 100
    },
    emoji: undefined
}
findUndefinedness(user);
//=> [ 'name', 'github.repositories.private', 'github.followers.repositories.private', 'emoji' ]