Node.js – Ajax Pagination without the Pages

Before starting, it's important that you have a basic knowledge of Node, the Express API, and as well Jade templating.  If you don't, take a quick gander at these previous introductory articles I've written:

• My First Node Application
• Node using Jade Templates with Express
• jquery HTML template

Now that you have the basics down, let's get started.  Firstly, let me layout the folder structure and files required to complete this example:

/
public/
js/
jquery.min.js
paging.js
views/
partials/
items.jade
items.json
index.jade
layout.jade
app.js

Most of the files should be pretty familiar from our previous examples.  The Jquery.min.js file can be included externally if you like or you can have a local copy included.  I'll provide examples for the remaining files.

The example below will create an array, if you're looking for information about JavaScript arrays I've compile an entire page dedicated with over 10 different examples that will considerably improve your skills with Javascript arrays.

Let's start with the app.js file:

var express = require('express'), jade = require('jade');
var app = express();
var fs = require('fs');
var items;
var itemsPerPage = 2;
var maxPages = 0;
fs.readFile('views/partials/items.json', 'utf8', function(error, data) {
items = JSON.parse(data);
maxPages = items.length / itemsPerPage;
});
var pub = __dirname + '/public';
app.use(app.router);
app.use(express.static(pub));
app.use(express.errorHandler());
app.set('views', __dirname + '/views');
app.set('view engine', 'jade');
app.get('/', function(req, res) {
res.render('index.jade', {
pageTitle: 'Test',
items: items.slice(0, 2),
maxPages: maxPages,
layout: true
});
});
app.get('/page/:page', function(req, res) {
var page = req.params.page;
var start = (page - 1) * 2;
var end = page * 2;
res.render('partials/items.jade', {
pageTitle: 'Test',
items: items.slice(start, end),
layout: false
});
});
app.listen(8000);

Hopefully you are not immediately overwhelmed by the code, once we break it down a bit more, it should make a lot of sense.

Lines 1 and 2 are the same as before, simply setting up Express and Jade.  Line 4 through 11 are doing something a little new.  I'm including the ability to use the file stream (fs) and reading the aforementioned items.json file.  Once the file is read, the JSON values are stored in the local variable items.  Once loaded, I'm also calculating the maximum pages that are to be displayed by dividing by the number of items I want per page, in this case 2.

Lines 13 through 19 are simply configuring Express and Jade to work together as well as configuring the public folder to serve any Javascript or CSS files that we might have. Something that might be good as a next step is how-to Access query string parameters with Express and Node.js.

And finally, lines 21 through 40 are two routes that have been setup to render the view and display the items on screen.  In the first route (/), I'm simply passing the first two items of the items array to the view.  Whereas, in the second route, based on the page request parameter, I'm calculating the start and end position of the items to display.

Next, let's create this mysterious views/partials/items.json file:

[
{"title": "My first title", "body": "Lorem ipsum dolor sit …"},
{"title": "My second title", "body": "Lorem ipsum dolor sit …"},
{"title": "My third title", "body": "Lorem ipsum dolor sit …"},
{"title": "My fourth title", "body": "Lorem ipsum dolor sit …"},
{"title": "My fifth title", "body": "Lorem ipsum dolor sit …"},
{"title": "My sixth title", "body": "Lorem ipsum dolor sit …"},
{"title": "My seventh title", "body": "Lorem ipsum dolor sit …"},
{"title": "My eighth title", "body": "Lorem ipsum dolor sit …"},
{"title": "My ninth title", "body": "Lorem ipsum dolor sit …"},
{"title": "My tenth title", "body": "Lorem ipsum dolor sit …"}
]

This file contains some placeholder dummy data in a JSON array containing a Javascript event handler with a title and body.  This will be used when I output the content.  In your own code, this would probably be something retrieved from your database…

Next, let's create the three view files mentioned above starting with the simplest, views/partials/items.jade:

#items
for item in items
.item
h2= item.title
p= item.body

This file outputs the title in an h2, the body in a p tag all wrapped in a div with the class of item and all wrapped in an outer div with the id of items.  The for loop is looping through the items variable that was passed to the layout from the app.js file.

Next is the basic views/index.jade file:

extends layout
block content
h2 Welcome
include partials/items

This file is pretty basic and just includes the previously created partial view.  The last view to create is the views/layout.jade file:

!!! 5
html(lang+"en")
head
title= pageTitle
block scripts
script
var maxPages= #{maxPages};
script(src='/js/jquery.min.js')
script(src='/js/paging.js')
style
#items { width: 300px; }
body
h1 Test
block content

The only noticeable thing happening above is on line 8 where I am creating a global variable called maxPages and setting it to the previously created maxPages variable that was calculated after loading the items.

You will also notice that I'm including a Javascript file called js/paging.js, this file should be created in your public directory as it contains the magic to perform the AJAX to request the next items:

var lastX = 0;
var currentX = 0;
var page = 1;
$(window).scroll(function () {
if (page < maxPages) {
currentX = $(window).scrollTop();
if (currentX - lastX > 200 * page) {
lastX = currentX;
page++;
$.get('/page/' + page, function(data) {
$('#items').append(data);
});
}
}
});

As a person scrolls down the page, I'm doing a calculation to determine if a new page should be loaded.  By keeping track of the last scroll position, the code is smart enough to not load additional content when the user scrolls up, and then back down again.

You can view the full source on GitHub here: https://github.com/endyourif/NodeDynamicPaging.

Published on Oct 15, 2012

Tags: AJAX | pagination | Node js Tutorial | JavaScript | jQuery Tutorial