1/
    (function($){
        $.extend({
            jYoutube: function( url, size ){
                if(url === null){ return ""; }
                size = (size === null) ? "big" : size;
                var vid;
                var results;
                results = url.match("[\\?&]v=([^&#]*)");
                vid = ( results === null ) ? url : results[1];
                if(size == "small"){
                    return "http://img.youtube.com/vi/"+vid+"/2.jpg";
                }else {
                    return "http://img.youtube.com/vi/"+vid+"/0.jpg";
                }
            }
        })
    })(jQuery);
    2/
    $.test = function(text)
    {
    $("#ahoj").text(text);
    }
    $.test("blaaaa");
    3/
    /*
    * jTwitter 1.1.1 - Twitter API abstraction plugin for jQuery
    *
    * Copyright (c) 2009 jQuery Howto
    *
    * Licensed under the GPL license:
    * http://www.gnu.org/licenses/gpl.html
    *
    * URL:
    * http://jquery-howto.blogspot.com
    *
    * Author URL:
    * http://jquery-howto.blogspot.com
    *
    */
    (function( $ ){
        $.extend( {
            jTwitter: function( username, numPosts, fnk ) {
                var info = {};
                
                // If no arguments are sent or only username is set
                if( username == 'undefined' || numPosts == 'undefined' ) {
                    return;
                } else if( $.isFunction( numPosts ) ) {
                    // If only username and callback function is set
                    fnk = numPosts;
                    numPosts = 5;
                }
                
                var url = "http://twitter.com/status/user_timeline/"
                    + username + ".json?count="+numPosts+"&callback=?";
                $.getJSON( url, function( data ){
                    if( $.isFunction( fnk ) ) {
                        fnk.call( this, data );
                    }
                });
            }
        });
    })( jQuery );
    --------------
    použití
    $(document).ready(function(){
    // Get latest 6 tweets by jQueryHowto
    $.jTwitter('jQueryHowto', 10, function(data){
    $('#posts').empty();
    $.each(data, function(i, post){
    $('#posts').append(
    '<div class="post">'
    +' <div class="txt">'
    // See output-demo.js file for details
    + post.text
    +' </div>'
    +'</div>'
    );
    });
    });
    });
    4/
    $.fn.makeRed = function() {
    return $(this).css('background', 'red');
    }
    $('#myTable').find('.firstColumn').makeRed().append('hello');
    5/
    $.extend(
    $.expr[':'],
    {
    over100pixels: function(a) {
    return $(a).height() > 100;
    }
    });
    $('.box:over100pixels').click(function() {
    alert('The element you clicked is over 100 pixels high');
    });