How do I get event.key to display each letter in my html?

Thank you for taking the time to help!

I am working on a hangman game and am running into a small issue. I am able to see the userInput if it is any other letter than what's below in my if else statements. The problem is that I want it to display that event, and then display any other event that wasn't already keyed to displayed alongside. For example: if userInput is === "k" then userInput is === "b", I would like it to keep the display of "k" in my html and then alongside it "b".

Also if there is a better way to write my if else statement with a loop or using forEach that would be helpful. I am new to the concepts. Thanks again.

   document.onkeyup = function(event) {
            var userInput = event.key;



        if (currentWord === "taco"){

            if (userInput === "t" ) { 

                document.getElementById("1st-letter").innerHTML = userInput;
            }

            else if (userInput === "a") {

                document.getElementById("2nd-letter").innerHTML = userInput;

                }

            else if (userInput === "c") {

                document.getElementById("3rd-letter").innerHTML = userInput;

            }

            else if (userInput === "o") {
                document.getElementById("4th-letter").innerHTML = userInput;
            }


            else {
                document.getElementById("incorrect-letters").innerHTML = userInput;

            }
        }
        else {
            alert("Code is working");
        }


};