jQuery Connect JS - A small script to make connections between two elements.

jquery.connect.js

// jQuery Connect v0.0.1
// (c) Zulfa Juniadi <http://zulfait.blogspot.com/>
// Usage : var connection = $.connect('#elem1', '#elem2', {options});
// Documentation : http://zulfait.blogspot.com/2013/07/jquery-connect.html
// Source : https://gist.github.com/zulfajuniadi/5928559#file-jquery-connect-js
// Requires : jQuery v1.9+ (Older versions may work, but not tested)
// Suggests : jQuery UI (It works with draggable elements!)
// MIT License

;(function($) {
    $.connect = function(elem1, elem2, options) {
        var defaults = {
            container: '#container',
            leftLabel: 'Left',
            rightLabel: 'Right',
        };
        var parent = this;
        this.elem1 = this.elem1 || $(elem1);
        this.elem2 = this.elem2 || $(elem2);
        if (elem1.length === 0 || elem2.length === 0) {
            throw 'Cannot get instance of Element 1 or Element 2';
        }
        var A = {};
        var B = {};
        var C = {};
        this.options = $.extend(defaults, options || {});
        var makeConnector = function(data) {
            var container = $(parent.options.container);
            var html = $('<div class="connector"><p class="left title"></p><p class="right title"></p></div>');
            if (typeof parent.Connector === 'undefined') {
                parent.Connector = html.appendTo(container);
                parent.Connector.css({
                    position: 'absolute',
                    width: '100px',
                    'border-bottom': '1px solid grey'
                });
                parent.Connector.find('p').css({
                    display: 'inline-block',
                    'margin-bottom': '-3px'
                });
                parent.Connector.find('.left').css({
                    float: 'left',
                    padding: '0 10px'
                });
                parent.Connector.find('.right').css({
                    float: 'right',
                    padding: '0 10px'
                });
                parent.setLabels(parent.options);
            }
            var topOffset = -20;
            if (A.coords.tc[0] > B.coords.tc[0]) {
                parent.Connector.find('.title').css({
                    '-webkit-transform': 'rotate(180deg)',
                    '-ms-transform': 'rotate(180deg)',
                    'transform': 'rotate(180deg)'
                });
            } else {
                parent.Connector.find('.title').css({
                    '-webkit-transform': 'rotate(0deg)',
                    '-ms-transform': 'rotate(0deg)',
                    'transform': 'rotate(0deg)'
                });
            }
            parent.Connector.css({
                top: C.sc[1] + topOffset + 'px',
                left: C.sc[0] + 'px',
                width: C.width + 'px',
                '-webkit-transform': 'rotate(' + C.angleA + 'deg)',
                '-webkit-transform-origin': '0% 100%',
                '-ms-transform': 'rotate(' + C.angleA + 'deg)',
                '-ms-transform-origin': '0% 100%',
                'transform': 'rotate(' + C.angleA + 'deg)',
                'transform-origin': '0% 100%'
            });
        };
        this.setLabels = function(values) {
            var defaults = {
                leftLabel: 'Left',
                rightLabel: 'Right'
            };
            var labels = $.extend(defaults, values);
            $(parent.Connector).find('.title').each(function(idx, elem) {
                var e = $(elem);
                if (e.hasClass('left')) {
                    e.html(labels.leftLabel);
                } else {
                    e.html(labels.rightLabel);
                }
            });
            return parent;
        };
        var getCoords = function(elem, width, height) {
            function pX(elem) {
                return elem.position().left;
            }
            function pY(elem) {
                return elem.position().top;
            }
            var px = pX(elem);
            var cen = px + (width / 2);
            var py = pY(elem);
            var mid = py + (height / 2);
            var ret = {
                tl: [px, py],
                tr: [px + width, py],
                tc: [cen, py],
                rm: [px + width, mid],
                bc: [cen, py + height],
                lm: [px, mid]
            };
            return ret;
        };
        this.calculate = function() {
            var elem1 = parent.elem1;
            var elem2 = parent.elem2;
            A.width = elem1.width();
            A.height = elem1.height();
            A.coords = getCoords(elem1, A.width, A.height);
            B.width = elem2.width();
            B.height = elem2.height();
            B.coords = getCoords(elem2, B.width, B.height);
            C.sc = A.coords.rm;
            C.ec = B.coords.lm;
            if ((B.coords.tl[0] - A.coords.tl[0] <= 90) && (B.coords.tl[0] - A.coords.tl[0] >= -90)) {
                if (B.coords.tc[1] <= A.coords.tc[1]) {
                    C.sc = A.coords.tc;
                    C.ec = B.coords.bc;
                } else {
                    C.sc = A.coords.bc;
                    C.ec = B.coords.tc;
                }
            } else if (B.coords.tc[0] <= A.coords.tc[0]) {
                C.sc = A.coords.lm;
                C.ec = B.coords.rm;
            }
            C.angleA = Math.atan((C.sc[1] - C.ec[1]) / (C.sc[0] - C.ec[0])) * 180 / Math.PI;
            if (B.coords.tc[0] <= A.coords.tc[0]) {
                C.angleA -= 180;
            }
            C.width = Math.sqrt(Math.pow(C.ec[0] - C.sc[0], 2) + Math.pow(C.ec[1] - C.sc[1], 2));
            makeConnector();
            return parent;
        };
        this.calculate();
        return this;
    };
})(jQuery);

A small patch to handle fixed elements: http://jsbin.com/judutugenaci/1/edit
I guess my code can probably be better.