Edit in JSFiddle

$("#login").click(function () {
    $(this).focus(); // Focus on the "Create User" button.
    var username = $("#username").val(); // Grab the Username
    var publicKey = $("#publicKey").val(); // Grab the Public Key

    // Make sure that something was entered for the Username and Public Key
    if (username.length > 0 && publicKey.length > 0) {
        // Initialize PubNub
        var pubnub = PUBNUB.init({
            publish_key: 'demo',
            subscribe_key: 'demo',
            uuid: username
        });

        // This function updates the table by calling here_now.
        var updateTable = function () {
            pubnub.here_now({
                channel: 'doge_key_exchange',
                state: true,
                callback: function (m) {
                    $("#here_now").html("<pre>// pubnub.here_now() returns...<br><br>" + JSON.stringify(m, undefined, 2) + "</pre>"); // Prints the results of the `here_now` call.
                    var table = $("tbody");
                    table.empty();

                    var foundSelf = false;
                    var str = "";
                    for (var i = 0; i < m.uuids.length; i++) {
                        var state = m.uuids[i].state;

                        str += "<tr><td>" + (i + 1) + "</td><td>" + state.username + "</td><td>" + state.publicKey + "</td></tr>";
                        if (state.username === username && state.publicKey === publicKey) {
                            foundSelf = true;
                            $("#username").val("");
                            $("#publicKey").val("");
                        }
                    }
                    table.append(str);
                    if (!foundSelf) {
                        // If the results of our here_now call 
                        // doesn't include ourself, try again.
                        updateTable();
                    }
                }
            });
        };

        pubnub.subscribe({
            channel: 'doge_key_exchange',
            callback: function (m) {
                console.log(m);
            },
            state: {
                username: username,
                publicKey: publicKey
            },
            presence: updateTable,
            heartbeat: 60
        });
    }
});


// Detect when the enter key is pressed
$(document).bind("enterKey", function () {
    if ($("#username").val().length === 0) {
        $("#username").focus();
    } else if ($("#publicKey").val().length === 0) {
        $("#publicKey").focus();
    } else {
        $("#login").click();
    }
});

$(document).keyup(function (e) {
    if (e.keyCode == 13) {
        $(this).trigger("enterKey");
    }
});

<div class="jumbotron">
    <h1>PubNub Key Exchange</h1> 
    <div class="container">
        <div class="row">
            <div class="col-md-6">
                <div class="input-group"> <span class="input-group-addon">Username</span>

                    <input id="username" type="text" class="form-control" placeholder="'doge'">
                </div>
            </div>
            <div class="col-md-6">
                <div class="input-group"> <span class="input-group-addon">Public Key</span>

                    <input id="publicKey" type="text" class="form-control" placeholder="'much_security'">
                </div>
            </div>
            <button id="login" type="button" class="btn btn-primary">Create User</button>
        </div>
    </div>
</div>
<div class="container">
    <div class="row">
        <div class="col-md-6">
            <table id="user_key" class="table table-hover">
                <thead>
                    <tr>
                        <th><strong>#</strong>

                        </th>
                        <th><strong>Username</strong>

                        </th>
                        <th><strong>Public Key</strong>

                        </th>
                    </tr>
                </thead>
                <tbody></tbody>
            </table>
        </div>
        <div class="col-md-6">
            <div id="here_now"> <pre>// pubnub.here_now() returns...</pre>

            </div>
        </div>
    </div>
</div>