1.js

var component = require('omniscient');
var React = require('react');
var immstruct = require('immstruct');

// With start time
var structure = immstruct({ startTime: new Date(), currentTime: new Date() });

var Timer = component(function (props) {
    // Or swap to have time until.
    return React.DOM.h1({}, 'MS since start: ' + (props.cursor.get('currentTime') - props.cursor.get('startTime')) );
});

var render = function () {
    React.render(Timer(structure.cursor()), document.body);
};

render();
structure.on('swap', render);


setInterval(function () {
    structure.cursor('currentTime').update(function () {
        return new Date();
    });
}, 1000 * 60); // Update every minute