showModalDialog

A popup that froze every script on the page until the visitor dealt with it, and then handed back a return value.

In 2026: Dead. Chrome removed it in 2014 and Firefox in 2017, because pausing the entire engine mid-function while a second page runs was a nightmare nobody wanted to maintain. The demo button now reports that showModalDialog is not a function. Its one honest descendant is the dialog element, which does the modal part without freezing the world.

Where it came from: Microsoft Internet Explorer 4, 1997. Removed from Chrome in 2014 and Firefox in 2017. MDN ↗

<script language="JavaScript">
function editDetails() {
  // Opens a dialog and STOPS EVERY SCRIPT until the visitor closes it,
  // then hands back whatever the dialog chose to return.
  var result = window.showModalDialog(
      "details.html", null,
      "dialogWidth:400px; dialogHeight:300px; status:no");
  alert("The dialog returned: " + result);
}
</script>

<button onclick="try { editDetails() } catch (e) {
  document.getElementById('out').innerHTML = e; }">Edit details</button>
<p id="out"></p>