I just don't understand $.fn in jQuery

What is wrong with this syntax?

<script>
jQuery(function() {
    jQuery.fn.myfunction(myparam) {
        alert(myparam);
        return 0; // return jQuery?
    }
    my开发者_高级运维function('Hello World');
});
</script>

I'm trying to learn how to extend jQuery.

jQuery.fn.myfunction(myparam) {

should be

jQuery.fn.myfunction = function(myparam) {

as you are assigning the property myfunction of object jQuery.fn a value of function () {...

Your syntax is trying to call a method called myFunction on the jQuery.fn reference.

To extend the jQuery object, you want this syntax:

<script>
jQuery(function() {
    jQuery.fn.myfunction = function(myparam) {
        alert(myparam);
        return this; // returns the current jQuery object.
    }

    // Select something with jQuery using the $() function here.
    $().myfunction('Hello World');
});
</script>

A method defined via jQuery.myFunction is a "static" function. You call it by doing $.yourFunction, and it's not tied to a result set.

Conversely, a function defined on jQuery.fn.myFunction is a tied to a result set; if you do "this" within that function, you'll get the jQuery object that was used to call it. In other words, if you do $("P").myFunction() "this" in my Function will be $("P").

From the documentation...

jQuery.fn.extend({
  check: function() {
    return this.each(function() { this.checked = true; });
  },
  uncheck: function() {
    return this.each(function() { this.checked = false; });
  }
});

See more here.