add onclick event javascript

var element = document.getElementById("elem");
element.onclick = function(event) {
  console.log(event);
}

 document.getElementById("myBtn").addEventListener("click", function(){
  document.getElementById("demo").innerHTML = "Hello World";
}); 

<script>
  $(document).ready(function(){
    $('#MyButton').click(function(){
       CapacityChart();
    });
  });
</script>

<input type="button" value="Capacity Chart" id="MyButton" >

object.addEventListener("click", myScript);

	<input type="text" name="text" id="test" onmouseover="skriv('klick')">
    <input type="button" name="send" value="Skicka" id="klick" onclick="skriv('test')">
    
    
    <script src="lib/script.js"></script>


// in lib/script.js

  function skriv(name) {
    document.getElementById(name).style.backgroundColor='red';
  }

<button onClick="script">

  <img src="hospital.png" id="hospitals" onclick="damarkers();">