Need help for a getInput function

I've been having trouble with my javascript code.

function getInput() {
    document.getElementById("enterInput").addEventListener("click", function() {
        return document.getElementById("inputLine").value;
        document.getElementById("inputline").value="";
    });
}

As you can probably see I want to get input from a <input type="text"> with the id of inputLine. And a button with the id of enterInput.

But all I get back is undefined, and I've been working on this for a long time, so I'm getting frustrated.

Sorry for bad english.