Total results: 30

Improve page performance with optimal CSS

There are certain CSS best practices that should be followed in order to increase CSS performance in the browser. These will help the browser to perform less DOM parsing and reduce the time of repaint events.

1. Browser reflow and repaint

If you are unfamiliar with the concepts of reflow and repaint, here are some articles that will get you up to speed:

2. Remove unused styles

Simply having styles that aren't used causes the browser to search the DOM for matches needlessly. This is wasted processor time. Additionally, the CSS file will have a higher page weight that is needlessly sent over the wire to the client.

It may not seem to make a huge difference but removing dead CSS code will greatly increase performance and additionally improve the project stability and maintainability.

Check size of localStorage usage in Chrome

localStorage is a great tool for JavaScript developers to persist information across multiple sessions. Due to its simple API, large browser support and and higher reliability than cookies, it can easily lead to the situation of overusing localStorage.

Since localStorage has a maximum size of 5MB the following snippet will help inspect what localStorage keys are being used and how much size is being allocated to each.

To give credit, I have taken the method here and added a total counter.

var total = 0;
for(var x in localStorage) {
  var amount = (localStorage[x].length * 2) / 1024 / 1024;
  total += amount;
  console.log( x + " = " + amount.toFixed(2) + " MB");
}
console.log( "Total: " + total.toFixed(2) + " MB");

Simply run this in the Chrome console or create a bookmarklet from the following code (Right click bookmark bar > Add Page > Copy the code as "URL")

javascript:var total = 0;for(var x in localStorage) {  var amount = (localStorage[x].length * 2) / 1024 / 1024;  total += amount;  console.log( x + "=" + amount.toFixed(2) + " MB");}console.log( "Total: " + total.toFixed(2) + " MB");

Which will give a similar output:

Matches = 0.40 MB
Matches_timestamp = 0.00 MB
Teams = 0.19 MB
Teams_timestamp = 0.00 MB
Total: 0.59 MB

Dynamically append LESS.js stylesheets

Here is a function that can be called to dynamically apply a LESS.js stylesheet to the DOM after the page has finished loading. The following code snippet uses jQuery for convenience.

 function loadLESS ( filename ) {
    // If LESS isn't available, do nothing
    if ( !window.less ) { return;}

    // Create LESS link and add to <head>
    var $link = $("<link type='text/css' rel='stylesheet/less' />");
    $link.attr("href", filename + ".less");
    $("head").append( $link );

    // Notify LESS that there is a new stylesheet
    less.sheets.push( $link[0] );
    less.refresh();
}

The important parts are after applying the new link tag to the head section, the raw DOM node $link[0] must be added to the less.sheets array and then refresh called to apply the changes to the web page.

Also remember that the rel attribute for the link tag must be set to "stylesheet/less" rather than just "stylesheet".

Append an HTML string to the DOM without a JavaScript Library

In the event where appending new nodes to the DOM via JavaScript is required but there is no access to a library such as jQuery or Prototype.JS, this handy snippet allows an easy librabry-like API with a tiny amount of code:

 function append ( elString, parent ) {
    var div = document.createElement( "div" );
    div.innerHTML = elString;
    document.querySelector( parent || "body" ).appendChild( div.firstChild );
 }

This snippet can be used easily:

// Append a link tag to the head
append( "<link rel='stylesheet' href='css/foo.css' />", "head" );

// Append a parapgraph to the body
append( "<p>My text</p>" );

// Append a new list item
append( "<li>Cheese</li>", "ul.shopping-list" );

Install Node.JS on Debian Wheezy

Official Method

The official Node.JS install guide recommends manually downloading and building the Node.JS package for Debian. This can be done using the following set of commands:

sudo apt-get install python g++ make checkinstall
mkdir ~/node_js_src && cd $_
wget -N http://nodejs.org/dist/node-latest.tar.gz
tar xzvf node-latest.tar.gz && cd node-v*
./configure
checkinstall
sudo dpkg -i node_*

This install method should work fine but will take a long time to complete on the Raspberry Pi's hardware. For this reason I experimented a little and found a quicker install method that doesn't require a manual compile, by using the Ubuntu package.

Ubuntu Method

This install method will be much faster than the official method but is not designed for Debian Wheezy, so use at your own risk! Personally I have not had any trouble with my node install yet but I cannot guarantee this will be the case for anyone else.

sudo apt-get update
sudo apt-get install -y python-software-properties python g++ make
sudo add-apt-repository ppa:chris-lea/node.js

At this point the file with the new repository details must be edited. Open the file: /etc/apt/sources.list.d/chris-lea-node_js-wheezy.list with a text editor like vim and change the word "wheezy" to "lucid". Thanks to Ken Yap for this hint.

Now, go on and finish installing Node.

sudo apt-get update
sudo apt-get install -y nodejs

A JavaScript Google Analytics event tracking plugin

In todays online world it is common for web developers to improve their websites by enabling a large amount of interactive functionality. Often this takes the form of JavaScript applications that no longer adhere to the simple page-by-page model but instead act more like a desktop program (Gmail, YouTube and Twitter for example).

If many interactions are happening in a single page without the URL changing, this experience is great for the user but can prove problematic when tracking for analytics. Traditionally analytics software such as Google Analytics is included in every web page of a site and each time a page is downloaded it is tracked back to Google. Obviously if the visitor never leaves that URL, this causes the aforementioned issue.

Google have a solution called "Events" that allow a developer to programmatically track an interaction via JavaScript. Events breakdown into the following components:

  • Category
  • Action
  • Label (optional)

For example, to track a customer checking out of an online store through a JavaScript form interface the following events may be used:

Format: Category / Action / Label

  1. Checkout / ViewCart
  2. Checkout / Country Selected / USA
  3. Checkout / Details Provided
  4. Checkout / Order Confirmed

From these tracked events, reports can be generated or funnels (called "Goals" by Google) setup to track conversion rates.

The method that Google provides to programmatically track an event looks as follows:

_gaq.push(['_trackEvent', 'Checkout', 'Country Selected', 'USA']);

This is simple enough, however, it is not wise to litter application code with calls to _gaq. If the Analytics script does not load due to a network issue this variable will be undefined and cause a potentially serious error. Also, if you someday remove Google Analytics it may be problematic to remove all occurrences of this throughout your code base.

For this reason I have created the following wrapper around the tracking code with a simple API and multiple advantages that can be plugged into any JavaScript application.

An effective LESS.js file include pattern

In the previous article I gave an introduction to CSS preprocessors and explained the potential advantages of using this technology. One of the mentioned examples was the ability to break down your stylesheet into multiple files and join them together to create a single final CSS file. This method provides a clean hierarchy for managing stylesheets.

My preferred pattern for the architecture of a preprocessed stylesheet is as follows:

  • Settings
  • Libraries
  • Modules
  • Views

First include the settings for my project (colours, fonts etc. in variables).

Secondly library code you have, for example, reset.css should be included.

Next I include my global styles and separate them into manageable modules. e.g. Links, Forms, Tables.

Finally I include my view related code for specific web pages and any overrides that are required. For example, a "view" could be the website home page as it usually differs from the rest of the website.

Example LESS.js Stylesheet

# screen.less

// Import settings
@include "settings/global.less";

// Import libraries
@include "libs/reset.css"; // Notice the .CSS extension

// Import global modules
@include "modules/core.less";
@include "modules/links.less";
@include "modules/forms.less";
@include "modules/site_header.less";
@include "modules/site_footer.less";

// Import views
@include "views/home.less";
@include "views/contact.less";
@include "views/admin.less";

Although the syntax is in LESS, this will also work with SASS using the import command

LESS/SASS: The Advantages of CSS Preprocessing Explained

CSS has a very powerful syntax but can easily become very verbose when working on non-trivial projects. In recent years the need to solve this problem has brought to life the concept of the CSS preprocessors such as SASS/SCSS and LESS.js. The former is written for the Ruby programming language whilst LESS is compiled using JavaScript.

A preprocessor allows additional leverage over CSS by providing additional syntax that delivers the following advantages:

  • Nested syntax

  • Ability to define variables

  • Ability to define mixins

  • Mathematical functions

  • Operational functions (such as “lighten” and “darken”)

  • Joining of multiple files

SCSS and LESS have very similar syntaxes, with SASS being a slight variant on SCSS. The similarities between them allows a developer to switch seamlessly if need be. In the following demonstration I will focus on the LESS syntax but all of the concepts can be transferred to the Ruby world.

Detect if page is within Facebook iframe or not: Javascript

Make sure to check the update at the end of the article. 

There is a handy piece of Javascript which you can use to tell if the current page is within the Facebook canvas iframe, or if it is being viewed normally in the browser.

The Facebook canvas gives its window a special "name" attribute. In most cases unless you generated the browsing window, it will have no name so we can use the piece of code below.

  if(window.name != "") {
    //We are on Facebook
  } 
  else
  {
    //We are just in the normal browser window
  }

However, if you changed your window name through Javascript, change the IF statement to match.

With this information, we can hide, add or manipulate our HTML in any way that is required to highlight the difference between your Facebook app and the regular web app.

 

Update Feb 2016:

As noted by Kilian in the comment section, an imporved way to detect the Facebook iframe is:

if(window.name.indexOf('iframe_canvas_fb') > -1)

© Blake Simpson, 2012 – 2018