Edit in JSFiddle

var AppState = function (initialState) {
    this.data = initialState;
    this.callbacks = [];
};

AppState.prototype.get = function () {
    return this.data;
};

AppState.prototype.set = function (newState) {
    this.data = newState;
    this.callbacks.forEach(function (cb) {
        cb.call(null, newState);
    });
};

AppState.prototype.addListener = function (cb) {
    this.callbacks.push(cb);
};

var PostsList = function (container, data) {
    this.container = container;
    this.setData(data);
};

PostsList.prototype.render = function () {
    var ul = document.createElement('ul');
    var lis = this.data.map(function (post) {
        var li = document.createElement('li');
        li.innerText = post.title;
        ul.appendChild(li);
    });
    while (this.container.hasChildNodes()) {
        this.container.removeChild(this.container.lastChild);
    }
    this.container.appendChild(ul);
};

PostsList.prototype.setData = function (newData) {
    this.data = newData;
    this.render();
};

var firstDataset = [{
    title: 'My new blog post'
}, {
    title: 'Managing state'
}];

var secondDataset = [{
    title: 'Updated blog post'
}, {
    title: 'New state'
}];

var datasets = [firstDataset, secondDataset];
var appState = new AppState(firstDataset);
var postsList = new PostsList(document.getElementById('main'), appState.get());

appState.addListener(function(newData) {
  postsList.setData(newData);
});

setInterval(function () {
    var idx = Math.round(Math.random(1));
    appState.set(datasets[idx]);
}, 500);

<div id="main"></div>