As functions are so integral to JavaScript, I have more examples of them below, this time using a switch case statement instead of a if/else statement. The functions do as described:
Function 1 calculates the percentage of a number based on what the user inputs and outputs to the users browser
Function 2 returns a message based on what the value is of the buttonName argument variable passed through, with another argument being the size of the drink itself and that reflected in the message
Function 3 returns the answer to a calculation based on what 2 numbers and an operator (+,-,*,/) are passed through the function as arguments.

JavaScript Code

        //Task 1 Function
        function percentageCalculator(number, percentage){
            let calculator = number * (percentage / 100);
            alert('Your answer is ' + calculator);
        }
        let number =  prompt('Enter a number');
        let percentage =  prompt('Enter a percentage');
        //Calling Task 1
        percentageCalculator(number, percentage);
        //Task 2 Function
        function drinkOrder(size, buttonName){
            let message;
            switch (buttonName){
                case 'cola':
                    message = 'You have ordered a ' + size + ' of Cola';
                    return message;
                case 'lemon':
                    message = 'You have ordered a ' + size + ' of Lemonade';
                    return message;
                case 'orange':
                    message = 'You have ordered a ' + size + ' of Orangeade';
                    return message;
                default:
                    return 'Incorrect type of drink';        
            }
        }
        let size = 'Medium';
        let buttonName = 'cola';
        //Calling Task 2
        console.log(drinkOrder(size,buttonName));
        //Task 3 Function
        function calculator(num1, num2, operator) {
            switch (operator) {
            case "+":
                return num1 + num2;
            case "-":
                return num1 - num2;
            case "*":
                return num1 * num2;
            case "/":
                return num1 / num2;
            default:
                return 'Invalid operator';
            }
        }
        //Calling Task 3
        console.log(calculator(5,4,'+'));
        console.log(calculator(5,4,'-'));
        console.log(calculator(5,4,'*'));
        console.log(calculator(5,4,'/'));