The Code

                    
                        // get the user input to reverse
                        function getValues() {
                            // get the text out of the input and assign it to a variable
                            let message = document.getElementById('userInput').value;
                      
                            // validate input and make sure its not empty
                            if (message.length == 0) {
                                // send a Swal message back if the input is not valid
                                Swal.fire(
                                    {
                                        backdrop: 'error',
                                        backdrop: false,
                                        text: 'Please enter a string to check'   
                                    }
                                );
                        
                            } else {
                        
                                // pass the user input to reverseMessage function 
                                // and assign it's return to a variable
                                let revMsg = reverseMessage(message);

                                // give th results to display messare
                                displayResults(message, revMsg);
                       
                            }
                        }
                        
                        // reverse the string
                        function reverseMessage(input) {
                        
                            // define return
                            let output = '';
                            
                            // use a for loop to provide the variable with details
                            for (let i = input.length - 1; i >= 0; i--) {
                                output += input[i];
                            }
                        
                            return output;
                        
                        }                                              
                        
                        function displayResults(msgEntered, revMsg) {
                        
                            document.getElementById('msg').textContent = `Your message is ${msgEntered}`;
                            document.getElementById('msg').textContent = `Your reversed message is ${revMsg}`;                                             
                        }                
                    
                

First we ask the user to input a value.

display message displays a sweetalert when the button is pressed and if the user has not entered a string to check