How could I make sure that at least one DIV is always shown?

Question

I have this piece of code I found that will show or hide a DIV using javascript. It only allows one div to be shown which is what I want. However, I want it where at least one DIV is always shown at a time. It basically toggles between hiding and showing them currently. I want it to be where if i hit DIV two again, it wont hide it and it will do nothing. Please help, thank you.

page.html

    <script src="scripts/pages.js"></script>
    <div class="main_div">
        <div class="inner_div">
            <div id="Div1">I'm Div One</div>
            <div id="Div2" style="display: none;">I'm Div Two</div>
            <div id="Div3" style="display: none;">I'm Div Three</div>
            <div id="Div4" style="display: none;">I'm Div Four</div>
        </div>
        <div class="buttons">
            <a href="#" onclick="divVisibility('Div1');">Div1</a> | 
            <a href="#" onclick="divVisibility('Div2');">Div2</a> | 
            <a href="#" onclick="divVisibility('Div3');">Div3</a> | 
            <a href="#" onclick="divVisibility('Div4');">Div4</a>
        </div>
    </div>

pages.js

var divs = ["Div1", "Div2", "Div3", "Div4"];
var visibleDivId = null;
function divVisibility(divId) {
  if(visibleDivId === divId) {
    visibleDivId = null;
  } else {
    visibleDivId = divId;
  }
  hideNonVisibleDivs();
}
function hideNonVisibleDivs() {
  var i, divId, div;
  for(i = 0; i < divs.length; i++) {
    divId = divs[i];
    div = document.getElementById(divId);
    if(visibleDivId === divId) {
      div.style.display = "block";
    } else {
      div.style.display = "none";
    }
  }
}

Answer 1

You can simplify your code to following. Where you hide all the divs and show the div corresponding to the clicked element.

 function divVisibility(divId) { document.querySelectorAll(".inner_div > div").forEach(e => e.style.display = 'none'); document.getElementById(divId).style.display = 'block'; } 

 <div class="main_div"> <div class="inner_div"> <div id="Div1">I'm Div One</div> <div id="Div2" style="display: none;">I'm Div Two</div> <div id="Div3" style="display: none;">I'm Div Three</div> <div id="Div4" style="display: none;">I'm Div Four</div> </div> <div class="buttons"> <a href="#" onclick="divVisibility('Div1');">Div1</a> | <a href="#" onclick="divVisibility('Div2');">Div2</a> | <a href="#" onclick="divVisibility('Div3');">Div3</a> | <a href="#" onclick="divVisibility('Div4');">Div4</a> </div> </div> 

Answer 2

The part that causes this function to hide a div is the setting of visibleDivId to null.

function divVisibility(divId) {
  if(visibleDivId === divId) {
    // visibleDivId = null;
  } else {
    visibleDivId = divId;
  }
  hideNonVisibleDivs();
}

Commenting that line out (see line 3) keeps the clicked div as the visibleDivId and the second function (hideNonVisibleDivs) won't hide it.