toggle element javascript

function myFunction() {
  var x = document.getElementById("myDIV");

    if (x.style.display 
=== "none") {
    x.style.display = "block";
  } else {
    x.style.display = 
  "none";
  }
} 

document.querySelector("#test").hidden = true;
document.querySelector("#test").hidden = false;

  $(document).ready(function() {
    $("#btnshow").click(function() {
      $("#imgshow").slideToggle();
    });
  })