Any interaction in the html called by Javascript are events. Those events can be triggered by buttons or links or any html tags. Events interaction can be click,mouseover, mouseout, mouseenter, mouseleave, mousemove, mouseup, blur, focus etc.

Example of Event Handler

Please see the following example, where we add an event click in a button.

    <input type="button" value="Click Me" onclick="alert('You just click me')"/>

Click the following button to see the quick demo.

There is an alternative way to add an event handler via javascript. You can use the following javascript code example.

// Note the btn is the id of the input button
var myButton = document.getElementById("btn");
myButton.onclick = function(){ 
   alert("You just click me");
};

//alternative you can use the built in addEventListener as well

myButton.addEventListerner("click", function(event){
   alert("You just click me");
});

How to remove the event handler?

If you are creating the dynamic event handler via javascript, you can just set the onclick value to null. See below example:

// Note the btn is the id of the input button
var myButton = document.getElementById("btn");
myButton.onclick = null;