post.js

var marked = require('marked');
var highlight = require('my-code-highlighter');

exports.render = function(el, text) {
	el.innerHTML = marked(text, { highlight: highlight });
};

posts.js

var ajax = require('imaginary-ajax-lib');

var postsURL = "example.com/posts"; // Assuming a constant location. This could be passed as an argument to exports.fetch instead

// Returns a promise of a post array
exports.fetch = function() {
	return ajax.get(postsURL)
		.then(function(posts) {
			// process posts if you want
			return posts;
		})
};

// I'm not implementing each, because "perform a function for each element of a promise of an array" is too generic an operation to be linked to posts.
// It should come with your promise lib or be implemented elsewhere

exports.addPost = function(post) {
	ajax.post(postsURL + "/new", post);
};

ui.js

var posts = require('./posts');
var post = require('./post');

var target = document.getElementById('posts');

posts.fetch()
	.then(function(data) {
		data.forEach(function (text) {
			var div = document.createElement('div');
			post.render(div, text);
			target.appendChild(div);
		});
	});