Resumé

JsRender as a Templating Solution

Cristian Merighi (Sunday, March 18, 2012)

Purely client-side implementation for a twitter feed-reader using JsRender along with "some" other javascript frameworks.

This article is obsolete. Some functionalities might not work anymore. Comments are disabled.

I want to conform myself to the confusing maelstrom ruling the world of javascript components and try to offer my personal two-cents solution about putting together (I mean PUTTING TOGETHER) a purely client-side Twitter parser.

Let me introduce the guys who'll help me to get my job done. They're MANY, some of them are issue-prones, some of them are wonderful at some aspects but miss (or gave up!) some others... (Fairly pissed off by the actual js world snapshot, does it show?)

Microsoft Ajax 4 (String.format, Date.parseInvariant, Array.insert...)
jQuery (Async calls, DOM manipulation, Utilities...)
JsRender (Templating, Data formatting...)
Other stuff (jQuery-relevant) of restricted utility...

Goal: using the Twitter REST Api to retrieve and display tweets in a fully comprehensive fashion (w/ avatars, hashtags, mentions and links), using just DHTML technologies (sorry for having resusciated this 20th century term).

Dissecting the code, let's start with the declarative JsRender template:

JsRender Template

<ul id="tweets" class="Tweets">
<li><div class="Loader"></div></li>
</ul>
<script id="twitTmpl" type="text/x-jsrender">
<li><img src="{{:user.profile_image_url_https}}" />{{:~renderTweet(#view)}}<span class="Date">{{:~timeago(created_at)}}</span></li>
</script>

I've highlighted the bindings to the tweet entity properties: user along with created_at are respectively a complex and a simple/plain "property" for the json tweet representation, on the other side #view wraps the whole entity object (looks like a DataItem coming from the ASP.Net WebForms environment).
JsRender syntax: {{:[_property_].[_subproperty_]}} (please notice there's no spaces between braces and colons, nor between colon and text!).
{{:~foofunc([_propertypath_or_view_])}} to adjust the output before the very rendering (foofunc is a "view helper method").

Where do these helper methods go (in the following code snippet they're named renderTweet e timeago)?

View Helper Methods

// "sort-of" converters
$.views.helpers({
// accepts the whole (wrapped) dataItem (aka "#view")
renderTweet: function (view) {
var tweet = view.data;
var txt = tweet.text;
var rettxt = '';
var entities = tweet.entities;
var trunks = [];
if (entities) {
// sorting the various entity trunks
$.each(entities.hashtags, function (i, hash) {
pushTrunk(trunks, { start: hash.indices[0], end: hash.indices[1], text: hash.text, type: 'hash' });
});
$.each(entities.urls, function (i, url) {
pushTrunk(trunks, { start: url.indices[0], end: url.indices[1], text: url.url, type: 'url' });
});
$.each(entities.user_mentions, function (i, usr) {
pushTrunk(trunks, { start: usr.indices[0], end: usr.indices[1], text: usr.screen_name, type: 'user' });
});
// assembling the final html string (rettxt)
var lastIndex = 0;
$.each(trunks, function (i, trunk) {
switch (trunk.type) {
case "hash":
rettxt += txt.substring(lastIndex, trunk.start) + "<a target=\"_blank\" href=\"https://twitter.com/search/%23" + trunk.text + "\">#" + trunk.text + "</a>";
break;
case "url":
rettxt += txt.substring(lastIndex, trunk.start) + "<a target=\"_blank\" href=\"" + trunk.text + "\">" + trunk.text + "</a>";
break;
case "user":
rettxt += txt.substring(lastIndex, trunk.start) + "<a target=\"_blank\" href=\"https://twitter.com/" + trunk.text + "\">@" + trunk.text + "</a>";
break;
}
lastIndex = trunk.end;
});
rettxt += txt.substring(lastIndex);
} else rettxt = txt;
return rettxt ;
},
timeago: function (createdAt) {
// using timeago plugin (issues with UTC date and L10N)
// Date.parseInvariant is exposed by Ajax 4
return $.timeago(Date.parseInvariant(createdAt, 'ddd MMM dd HH:mm:ss +0000 yyyy'));
}
});

Please notice the specific framework lures in the code comments.

As a glue for bridging the declarative-template and the helping methods is the following javascript code-block (please pay attention to the highlighted lines of code and to the respective - sometimes subtle - meaning reported in each preceding line of comment):

Glue Code

function loadTweets() {
// obey to cross-site-scripting issues
$.support.cors = true;
// format url using Ajax 4 String.format
var rest_url = String.format("https://api.twitter.com/1/statuses/user_timeline.json?include_entities=true&include_rts=true&screen_name={0}&count={1}", 'cmerighi', 3);
// jQuery ajax (fluent version)
$.ajax({
// be sure to specify dataType jsonp
dataType: "jsonp",
url: rest_url
}).success(function (tweets) {
// build up
// FIRST jsrender template...
$.templates({ twit: '#twitTmpl' });
// ...THEN the DOM
$('#tweets').empty().append($.render.twit(tweets));
}).error(function (e) {
alert(e.statusText);
}).always(function(){ /* runs anyway */ });
}