Strophe.addConnectionPlugin('logger', {
    // logs raw stanzas and makes them available for download as JSON
    connection: null,
    log: [],
    init: function (conn) {
        this.connection = conn;
        this.connection.rawInput = this.log_incoming.bind(this);;
        this.connection.rawOutput = this.log_outgoing.bind(this);;
    },
    log_incoming: function (stanza) {
        this.log.push([new Date().getTime(), 'incoming', stanza]);
    },
    log_outgoing: function (stanza) {
        this.log.push([new Date().getTime(), 'outgoing', stanza]);
    },
    // <a onclick="connection.logger.dump(event.target);">my download button</a>
    dump: function (what, filename){
        what.download = filename || 'xmpplog.json';
        what.href = 'data:application/json;charset=utf-8,\n';
        what.href += encodeURIComponent(JSON.stringify(this.log, null, '  '));
        return true;
    }
});