Anchor tags href isn't working when iframe is

We have opened an iframe in model dialog. In the iframe we are loading a document. The document is also and html page. The <a> tags in the document are not navigating to the id mentioned in their href.

Just a sample from the html document. Below is the <a> example,

<a data-custom-class="link" href="#infoshare">
  2. WILL YOUR INFORMATION BE SHARED WITH ANYONE?
</a>


<p id="infoshare" style="font-size:15px;">
  <span style="color: rgb(0, 0, 0);">
    <strong>
      <span style="font-size: 19px;">
        <span data-custom-class="heading_1">
          2. WILL YOUR INFORMATION BE SHARED WITH ANYONE?
        </span>
      </span>&nbsp;
    </strong>&nbsp;
  </span>
</p>

Onclick of the <a> it should navigate to the <p>.

Though, It works perfectly when the url is browsed in the browser.

But Doesn't work in the dialog model.

var modal = document.getElementById('myModal');

// Get the button that opens the modal
var btn = document.getElementById("infoshare");

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// When the user clicks the button, open the modal 
btn.onclick = function() {
  modal.style.display = "block";
}

// When the user clicks on <span> (x), close the modal
span.onclick = function() {
  modal.style.display = "none";
}

// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}

.modal {
  display: none; 
  position: fixed;
  z-index: 1; 
  padding-top: 100px;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: rgb(0,0,0); 
  background-color: rgba(0,0,0,0.4);
}
.modal-content {
  background-color: #fefefe;
  margin: auto;
  padding: 20px;
  border: 1px solid #888;
  width: 80%;
}

.close {
  color: #aaaaaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}

<a data-custom-class="link"  id="infoshare">
  2. WILL YOUR INFORMATION BE SHARED WITH ANYONE?
</a>
<div id="myModal" class="modal">

  <!-- Modal content -->
  <div class="modal-content">
    <span class="close">&times;</span>
    <p>Some text in the Modal..</p>
  </div>

</div>