Add:

function solution(num1) {
    return function (num2) {
        return num1 + num2;
    };
}

let add5 = solution(5);
console.log(add5(2));
console.log(add5(3));

FilterEmployees:

function solution(string, criteria) {
    let data;
    let propName, propValue;
    const isNotAll = criteria !== 'all';

    if (isNotAll) {
        [propName, propValue] = criteria.split('-');
        // Additional validation when propName or propValue are falsy
        if (!propValue || !propValue) {
            throw new Error('Criteria are in wrong format! Invalid criteria!');
        }
    }

    try {
        data = JSON.parse(string);
    } catch (error) {
        data = [];
    }

    data.filter(function (i) {

        return isNotAll ? i[propName] === propValue : true;
    }).forEach((item, index) => console.log(`${index}. ${item.first_name} ${item.last_name} - ${item.email}`));
}

const jsonData = `[
    {
        "id": "1",
        "first_name": "Ardine",
        "last_name": "Bassam",
        "email": "abassam0@cnn.com",
        "gender": "Female"
    }, {
        "id": "2",
        "first_name": "Kizzee",
        "last_name": "Jost",
        "email": "kjost1@forbes.com",
        "gender": "Female"
    },
    {
        "id": "3",
        "first_name": "Evanne",
        "last_name": "Maldin",
        "email": "emaldin2@hostgator.com",
        "gender": "Male"
    }
]`;

const r2 = solution(jsonData, 'gender-Female');