تمرین فانکشن های سفارشی در جاوااسکریپت

                "" printJavascript() {
    console.log("سلام جاوااسکریپت ");
}

                function printJavascript() {
    console.log("سلام جاوااسکریپت ");
}

""

                function printString("") {
    console.log(inputString);
}

printString("سلام جاوااسکریپت ");

                function doubleNumber(number) {
    var result = number * 2;
    "" result;
}

var result = doubleNumber(5);
console.log(result);

                function doubleNumber(number) {
    // result = number * 2
    // return result
    "";
}

var result = doubleNumber(5);
console.log(result);

                function isPositive(number) {
    if (number > 0) {
        return true;
    }
    else {
        return false;
    }
}

                function calculateShippingCost(weight, destination) {
    if (weight <= 0) {
        return "وزن نامعتبر است";
    }

    if (destination === "iran") {
        var shippingCost = 2 * weight;
        return shippingCost.toString();
    }

    if (destination === "international") {
        var shippingCost = 6 * weight;
        return shippingCost.toString();
    }

    return "مقصد نامعتبر است";
}

var weight = 3;
var destination = "international";
var result = calculateShippingCost(weight, destination);

console.log(result);

                functon checkNumber(number) {
    if (number > 0) {
        return "عدد مثبت است";
    }
    else if (number < 0) {
        return "عدد منفی است";
    }
    else {
        return "عدد صفر است";
    }
}

var result = checkNumber(20);
console.log(result);

                function checkNumber(number) {
    if (number > 0) {
        return "عدد مثبت است";
    }
    else if (number < 0) {
        return "عدد منفی است";
    }
   
    return "عدد صفر است";
}

var result = checkNumber(0);
console.log(result);

                function generateUsername(firstName, lastName, separator) {
    var username = firstName + separator + lastName;
    return username;
}

var firstName = "Emma";
var lastName = "Smith";
var result = generateUsername(firstName, lastName, "_");

console.log(result);

                function generateUsername(firstName, lastName, separator = "_") {
    var username = firstName + separator + lastName;
    return username;
}

var firstName = "Emma";
var lastName = "Smith";
var result = generateUsername(firstName, lastName, ".");

console.log(result);

                function generateUsername(firstName, lastName, separator = '_') {
    var username = `${firstName}${separator}${lastName}`;
    return username;
}

var firstName = 'Emma';
var lastName = 'Smith';
var result = generateUsername(firstName, lastName);

console.log(result);