Calling a User Defined Function in jQuery

Just try this. It always works.

$(document).ready(function() {
  $('#btnSun').click(function() {
    $.fn.myFunction();
  });
  $.fn.myFunction = function() {
    alert('hi');
  }
});

<script src=""></script>
<button id="btnSun">Say hello!</button>

They are called plugins, as Jaboc commented. To make sense, plugin function should do something with the element it is called through. Consider the following:

jQuery.fn.make_me_red = function() {
    return this.each(function() {
        this.style.color = 'red';
    });
};

$('a').make_me_red();

The following is the right method

$(document).ready(function() {
    $('#btnSun').click(function(){
        $(this).myFunction();
     });
     $.fn.myFunction = function() { 
        alert('hi'); 
     }
});

Try this $('div').myFunction();

This should work

$(document).ready(function() {
 $('#btnSun').click(function(){
  myFunction();
 });

function myFunction()
{
alert('hi');
}

jQuery.fn.make_me_red = function() {
    return this.each(function() {
        this.style.color = 'red';
    });
};

$('a').make_me_red() // - instead of this you can use $(this).make_me_red() instead for better readability.

$(document).ready(function() {
  $('#btnSun').click(function(){

      myFunction();

   });

   $.fn.myFunction = function() { 
     alert('hi'); 

    }; 
});

Put ' ; ' after function definition...

jQuery.fn.make_me_red = function() {
    alert($(this).attr('id'));
    $(this).siblings("#hello").toggle();
}
$("#user_button").click(function(){
    //$(this).siblings(".hello").make_me_red(); 
    $(this).make_me_red(); 
    $(this).addClass("active");
});
​

Function declaration and callback in jQuery.

jQuery.fn.clear = function()
{
    var $form = $(this);

    $form.find('input:text, input:password, input:file, textarea').val('');
    $form.find('select option:selected').removeAttr('selected');
    $form.find('input:checkbox, input:radio').removeAttr('checked');

    return this;
}; 


$('#my-form').clear();

in my case I did

function myFunc() {
  console.log('myFunc', $(this));
}
$("selector").on("click", "selector", function(e) {
  e.preventDefault();
  myFunc.call(this);
});

properly calls myFunc with the correct this.