How to call the click JavaScript event when pressing a button?

Not really sure what you need but clicking on the button below fires the alert. Put any function (event) in there.

https://jsfiddle.net/9p70hwyL/

<button type="submit" onclick="alert('The event')">Turn to the dark side</button>

You can do this :

<button id="target" onclick="myFunction()">Click me</button>

Or with jquery :

$( "#target" ).click(function() {
  alert( "Handler for .click() called." );
});

In Javascript, you can write the code in following two ways

<button type="submit" click="alert('Hi');">Turn to the dark side</button>

OR

    <button type="submit" click="buttonClicked();">Turn to the dark side</button>
function buttonClicked() {
   alert('Hi');
}

In Jquery, you can call event by class name (css class) and id.

<button type="submit" id="btn">Turn to the dark side</button>

$("#btn").click({
   alert('Hi');
});

OR

<button type="submit" class="btnClass">Turn to the dark side</button>

$(".btnClass").click({
   alert('Hi');
});

Here is what you need in JavaScript.

function submitForm(){
document.body.style.backgroundColor = "red";
}

#bg{
  width: 200px;
  height: 200px;
  background: green;
}

<div id="bg" ></div> 

<form action="#" method="get">
    <button onclick="submitForm()" type="button">Turn to the dark side</button>
</form>

In Javascript you can write the code in following

    <script>
     function clickMe(){
     alert("Hello World");
    }
    </script>

Theres the html onClick() method.

For example

<button onClick="return sampleFunction()">Click me!!!</button>

In JavaScript

function sampleFunction()
{ 
    alert("abc"); 
    return false;
}

This return false will stop the button's default action, for example like form posting. If you return true, it'll continue.

I'm sorry but it did not help me. Look at this:

    <form action="http://youtube.com" method="get">
  <ul>
    <li>
      <input id="checkbox_vader" type="checkbox" name="character" value="dark_side">
      <label for="checkbox_vader" data-sentence="There is no escape from the Dark Side.">Vader</label>
    </li>
  </ul>
  <button type="submit">Turn to the dark side</button>
</form>

I would like to do if-else in javascript/jquery. Please, can u told me, how to start writing code in js / jq?