JAVASCRIPT: replace iframe with new one or make new one if not exists

I need to replace iframe src acording to user input. I need some if else but not sure what to do with vars - I'm noob. Here is a code so far:

<div>
            
            <h3>Some Header</h3>
            
<input type="text" size="25" id="inputTxt" value="">
<button onclick="myFunc()">go</button>
<br>
<br>

<div id="myDiv"></div>

<script>
function myFunc() {
            var word = document.getElementById("inputTxt").value;
            //if iframe (iframeClass) exists - replace with new one - else make new one...
            var someNewFrame = document.createElement("iframe");
            someNewFrame.setAttribute("class", "iframeClass");
            someNewFrame.setAttribute("src", "http://someones.com/next/staters/" + word );
            var newFrame = document.getElementById("myDiv");
            newFrame.appendChild(someNewFrame); 
}
</script>

            
            </div>