Desarrollo Front End : directrices



What’s Up, DOCTYPE?

The absence of a DOCTYPE is a crime punishable by death. You may have relied on the following DOCTYPE in the past, but it’s important to know that this is now being superseded by a leaner and meaner snippet.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

Ideally, the HTML5 DOCTYPE should be used. It’s supported in all modern browsers, and throws IE6 and IE7 into standards modeSource.

<!DOCTYPE html>

Write Valid Semantic Markup

Writing websites with clean, semantic HTML is something we wish we could always do. Sometimes we find ourselves limited by the way pages were setup by our predecessors, or sometimes we’re coding an HTML email. The validity of the HTML should never be compromised, even if to solve a browser specific bug.

Headings should be heirarchically created from <h2> onwards, paragraphs should always be in <p> tags and so on and so forth. If you write semantic HTML, the resultant page will be cleaner, lighter and easily parsed by search engine spiders. This is one of the simplest SEO fixes you can undertake.


<span class="sectionHeading">A Heading</span>
<br /> <br />
Lorem ipsum dolor sit amet. ...
<br /> <br />


<h2>A Heading</h2>
	Lorem ipsum dolor sit amet. ...

Fallbacks for Middle Mouse Clicks

One of the most frustrating accessibility and usability flaws of the modern web stems from the remapping of hyperlink click functions. Elements that appear to be hyperlinks may have their single click functionality remapped via JavaScript, breaking middle mouse click (open in new tab) functionality. If they can be opened in a new tab, their href of a single hash sends you back to the same page.

A modern example of a popular website that is contributing to this problem is the Twitter web app. Middle mouse clicking of names or user avatars yields completely different results throughout the web app.

<!-- The old way, breaking the web -->
<a href="#"></a>

<!-- If you can't deliver a page on mouse click, it's not a hyperlink -->
<span class="link" role="link"></span>

Another alternative is the use of “hashbangs“, that remap normal URLs to hash links and fetch pages via AJAX. Libraries that provide hashbang functionality should be able to display the page normally when middle mouse clicked, or load the content from that page into a designated area when clicked normally. But tread carefully, there are plenty of people who believe hashbangs are breaking the web.

Use Microformats

Microformats are a way of making contact information machine readable. hCard classes (not vCard) are used to define the type of content contained within elements. These are then extracted or highlighted by the browser.

<span class="tel">
	<span class="type">home</span>:
	<span class="value">+1.415.555.1212</span>

If you were to navigate to a page that uses this, you would notice that a program like Skype will easily detect what numbers on the page are phone numbers. Mobile Safari does something similar on iOS devices.

For more information:

Images Need ‘Alt’ Text

The <img> tag requires alt text to both validate and meet accessibility guidelines. The text in the alt attribute should be descriptive of what the image shows, or is trying to achieve, unless of course the image is not critical.

If the image is of a list bullet or other trivial icons, it is recommended to simply leave the alt attribute empty, but still present. A screenreader will then ignore it, as opposed to having to read out “bullet” 20 times.

<img src="dog.gif" alt="Fido and I at the park!" />
<!-- good, descriptive -->

<img src="bullet.gif" alt="bullet" />
<!-- bad, as silly as it seems -->

<img src="bullet.gif" alt="" />
<!-- good -->

Use Tables for Tabular Data Only

Tables should only ever be used for the presentation of tabular data. The only exception is when composing HTML email, in which a table is almost the only thing supported by soul crushing email clients.

For accessibility, table headers should always be presented using <th> elements. Remember to also set cellpadding,cellspacing and border values to 0 as these are more consistently controlled by CSS.

<table cellpadding="0" cellspacing="0" border="0">
				Cell Header
				Cell Item

Use jQuery & jQuery UI Widgets

jQuery and jQuery UI are constructed to look and behave as close to identical as possible on different browsers. jQuery UI is designed to be WAI WCAG 2.0 and WAI ARIA compliant, so using the framework removes any uncertainty about plugins or scripts running on your site.


Whitespacing & Formatting

Any discussion about formatting, whitespacing and the placement of braces is going to be hotly debated. I guess the simplest rule is that, unless you’re willing to completely format a whole document, respect and maintain the formatting of an existing document. That means: see same-line braces throughout a JS file, continue to write code with same-line braces. Your code should fail the code review process if it doesn’t maintain consistency with the rest of the document.

Consistent formatting makes code more readable, and also means the code can be easily modified with find and replace commands. The coding habits we have picked up are thankfully very similar to what jQuery officially encourages. There are a few minor discrepencies, but again, these are personal issues or things that we think cannot be maintained. Further Reading


// Bad

// Good :)
if (blah === "foo") {


// Bad
if (foo)

// Good :)
if (foo) {


// Bad
if (foo)

// Good :)
if (foo) {


Strings should always use double quotes. Some people are very fond of their C style strings (single quotes), but this leads to conflicting styles within a script. C style string handling dictates that empty and single character strings should be wrapped in single quotations, while phrases and words should be wrapped in double quotations.


The requirement to comment code obsessively was pioneered by managers, team leaders and other people that interact with code infrequently. It is sought merely as a check box for an employee’s KPIs, and provides little return for the time spent doing so.

If a best-practice oriented developer follows the guidelines established in this document, their code should become so readable and obvious that the need to comment what it is doing is embarassingly redundant. Consider the following example. In this: booleans are posed as questions, and functions are named intuitively.

if (user.hasPermission) {

Commenting, in this scenario at least, is completely unnecessary.


Some parts of a project will never be easy to scan and understand. Consider a complicated regular expression, or a math function calculating angles or switching between degrees and radians. Without the comment above, beginner and intermediate readers will be fairly clueless to the scripts’ meaning.

// RegEx for validating US phone numbers, can be (XXX) XXX-XXXX (with or without dashes, spaces or brackets)
var phoneRegEx = /^(?(d{3}))?[- ]?(d{3})[- ]?(d{4})$/;

Always Use === Comparison

The use of the == equality operator allows for frustrating bugs to slip through almost undetected. It allows for weak typing that is best explained by JavaScript Garden. The use of the strict equality operator === does not run type coercion and therefore strictly evaluates the difference between two objects. Again, consult JavaScript Garden for more information

var zeroAsAString = "0";

if (zeroAsAString == 0) {
	// gets in here lolwut

if (zeroAsAString === 0) {
	// never gets in here


Double equals comparison is allowed when comparing to null, because it will detect both null or undefined properties. If you don’t fully understand this, I still suggest you use triple equals.

var foo = null;

// foo is null, but bar is undefined as it has not been declared
if (foo == null && bar == null) {
	// still got in here

Always Specify the Second ‘radix’ Parameter When Using .parseInt()

When parsing a string to an integer, it is considered good practice to specify the second ‘radix’ parameter – which determines to what base the string should be converted to. The default setting will trigger a radix of 16 whenever the string is lead by a 0. Most beginner and intermediate users are only ever going to be using a radix of 10. Thanks to João Moreno for logging thecorrection.

alert( parseInt("08") ); // alerts: 2

alert( parseInt("08", 10) ); // alerts: 8

Avoid Comparing to true and false

Direct comparison to the values of true and false is unnecessary. Sometimes it might be good for clarity, but it’s just extra code.

if (foo === true) {
	// good that they're using triple equals, bad as it's redundant

if (foo) {
	// yay!

if (!bar) {
	// the opposite

Avoid Polluting the Global Namespace

An over-reliance on global variables is something all of us, myself especially, are guilty of. Arguments as to why globals are bad are fairly straight forward: the chance of script and variable conflicts is increased, and both the source file and the namespace itself become littered with countless ambiguously named variables.

Douglas Crockford believes that the quality of a JavaScript application can be assessed by the number of global variables it uses; the less the better. Given that not everything can be a local (but let’s be honest, that one you’re thinking about right now, it can, don’t be lazy) you need to find a way of structuring your variables to prevent clashes and minimise the bloat. The easiest way is to employ a single variable or a minimal amount of modules on which the variables are set. Crockford mentions that YUI uses a single global, YAHOO. He discusses this in more detail in his blog post “Global Domination”.

Considering that, in the case of small web apps, globals are generally used to store application-wide settings: it’s generally better to namespace your project or settings as objects.

// polluted global name space
var settingA = true;
var settingB = false;
var settingC = "test";

// a settings namespace
var settings = {
	settingA: true,
	settingB: false,
	settingC: "test"

But if we’re avoiding globals to reduce the chance of conflicts, isn’t standardising the namespaces to be the same going to increase chance of one app’s settings overwriting anothers? Well, it would make sense. It is instead suggested that you namespace your globals to your own specific app name, or reassign your namespace much in the same way that jQuery uses$.noConflict() mode.

var myAppName = {
	settings: {
		settingA: true

//accessed as
myAppName.settings.settingA; // true

Camel Case Variables

The camel casing (or camelCasing) of JavaScript variables is accepted as the standard in most coding environments. The only exception that was raised in the comment section is the use of uppercase and underscores to denote contants.

var X_Position = obj.scrollLeft;

var xPosition = obj.scrollLeft; // tidier

SCENE_GRAVITY = 1; // constant

Loop Performance – Cache Array Length

Looping is arguably the most important part of JavaScript performance to get right. Shave a millisecond or two off inside of a loop, potentially gain seconds overall. One such way is to cache the length of an array so it doesnt have to be calculated every time the loop is iterated through.

var toLoop = new Array(1000);

for (var i = 0; i < toLoop.length; i++) {
	// BAD - the length has to be evaluated 1000 times

for (var i = 0, len = toLoop.length; i < len; i++) {
	// GOOD - the length is only looked up once and then cached


If you’re looping through an array to find an remove a particular item, this will alter the array length. Any time you change the array length by either adding or removing items from inside the loop, you will get yourself into trouble. Consider either re-setting the length or avoid caching it for this particular situation

Loop Performance – Use ‘break;’ & ‘continue;’

The ability to step over and out of loops is really useful in avoiding costly loop cycles.

If you’re looking for something inside of a loop, what do you do once you find it? Say the condition you’re looking for is matched halfway through a 1000 item loop. Do you execute whatever you intend to do, and allow the loop to continue to iterate over the remaining 500 items, knowing that there’s no chance it will hit an if statement? Nope! You break out of your loop, literally!

var bigArray = new Array(1000);

for (var i = 0, len = bigArray.length; i < len; i++) {
	if (i === 500) {
	console.log(i); // will only log out 0 - 499

Another problem is skipping over a particular iteration and then continuing on with the loop. While things like odds and evens are better managed by replacing i++ with i + 2, some conditions need to be specifically listened for, to then trigger the skip. Anything that prevent’s running through an entire iteration is pretty handy.

var bigArray = new Array(1000);

for (var i = 0, len = bigArray.length; i < len; i++) {
	if (condition) {

Don’t Send Too Many Function Parameters

This is a pretty bad idea, more for readability than anything:

function greet(name, language, age, gender, hairColour, eyeColour) {

It’s a much better idea to construct an object before-hand or to pass the object inline

function greet(user) {

	name: "Bob",
	gender: "male"

Remap ‘this’ to ‘self’

When writing object-oriented (OO) JavaScript, the scope of this must be understood. Regardless of what design pattern you choose to structure your pseudo-classes, a reference to this is generally the easiest way to refer back to an instance. The moment you begin integrating jQuery helper methods with your pseudo-classes is the moment you notice the changing scope of this.


Person.prototype.findFriend = function(toFind) {
	// this = Bob
	$(this.friends).each(function() {
		// this = Bob.friends[i]
		if ( === toFind) {
			// this = Barry
			return this;

In the above example, this has changed from a reference to Bob, to his friend Barry. It’s important to understand what happened to the value of this over time. Inside of the prototyped function, this refers to the instance of the pseudo-class (in this case Bob). Once we step inside the $.each() loop, this is then re-mapped to be item i in the parsed array.

The solution is to remap the value of this to either self or _self. While self (sans underscore) is not exactly a reserved keyword, it is a property of the window object. Although my use of self was picked up from the jQuery source code, they have realised their mistake and are attempting to rectify the situation and instead use _self. Personally, I prefer the use of self for the sheer cleanliness – but it can throw some pretty confusing bugs for people. Tread carefully.

In the following example I will better utilise the parameters made available with the $.each() helper, as well as re-mapping the value of this.


Person.prototype.findFriend = function(toFind) {

	// the only time "this" is used
	var _self = this; 

	$(_self.friends).each(function(i,item) {
		if ( === toFind) {
			return item;


CanIHaz Boolean?

Booleans should be easily identifiable by the way they are named. Use prefixes like iscan or has to propose a question.

isEditing = true;

obj.canEdit = true;

user.hasPermission = true;

Minimising Repaints & Reflows

Repaints and reflows relate to the process of re-rendering the DOM when particular properties or elements are altered. Repaints are triggered when an element’s look is changed without altering its layout. Nicole Sullivan describes these changes in a thorough blog post as style changes such as visibility or background-color. Reflows are the more costly alternative, caused by changes that alter the layout of the page. Examples include the addition or removal of elements, changes to an element’s width or height, and even resizing the browser window. Worst yet is the domino effect of reflows that cause ancestor, sibling and child elements to reflow.

There is no doubt that both reflows and repaints should be avoided if possible, but how?


It’s not that the following snippet is “bad code” exactly. But let’s assume that the array arr has 10 items.

var myList = document.getElementById("myList");

for (var i = 0, len = arr.length; i < len; i++) {

	myList.innerHTML += "<li>" + arr[i].title + "</li>"; //reflow - appending to element


In the above for loop, a reflow will be triggered for every iteration of the loop. 10 iterations cause 10 reflows.

Now consider the following:

var constructedHTML = "";

for (var i = 0, len = arr.length; i < len; i++) {
	constructedHTML += "<li>" + arr[i].title + "</li>"; //no reflow - appending to string

document.getElementById("myList").innerHTML = constructedHTML; //reflow

In this scenario, the elements are being constructed within a string. Not a single reflow is created by the loop, as the DOM is not being altered. Only once the array has been completely looped through is the string then applied as the innerHTML of an object, causing the only reflow of the function.

There are endless types of reflows and repaints that can be avoided, and lucky you gets to go on an read about them. Reading material on the subject matter is plentiful, but most of it is linked to from the excellent starting point that is Nicole Sullivan’s blog post. There are important lessons to be taken away from this when it comes to a multitude of technologies synonymous with “web 3.0” and HTML5. The lesson above can be directly applied to writing jQuery. It’s also important to consider when fiddling with canvas, and trying to keep a frame rate in the 30-60 range.

Don’t Use Milliseconds to Generate Unique IDs

There is a method for generating unique IDs that has hung around since the early days of web dev. It involved appending the elapsed milliseconds since January 1, 1970 to your static ID by way of:

var myID = "static" + new Date().getTime();

This was a fairly foolproof method originally, because even if two ofthe above lines were performed one after the other, a few millisecondsnormally separated their execution. New browsers brought with them newJavaScript engines, coupled with ever increasing clock speed. Thesedays it’s more likely that your milliseconds match than are slightlyincremented.

This leads to bugs that are near impossible to debug by conventionalmeans. Because your DOM is created on the fly, traditional validationof the page source won’t identify multiple IDs as an error. JavaScriptand iQuery error handling dictates that the first match for the IDwill be utilised and other matches ignored. So it doesn’t even throw aJS error!

No, the only real method to debug it is line by line breakpoint ingand logging – but “pause” at the wrong line and your milliseconds willno longer clash!

The good thing is that there are plenty of alternatives. To be pedantic, it’s worth noting that a computer’s random function is not truly random as it is seeded by system time- but the probability of clashes is rather minuscule.

var myID = "static" + Math.round(Math.random() * 10000);

Personally, I’m partial to a bit of faux GUID generation. Technicallya GUID is generated according to your hardware, but this JavaScriptfunction does the next best thing. The following is a handy function I’ve pinched from a stack overflow post.

function S4() {
   return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
function guid() {
   return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
var myID = "static" + guid();

Feature Sniff, Don’t Browser Sniff

Does the client’s browser support geolocation? Does the client’s browser support web workers? HTML5 video? HTML5 audio? The answer used to be:

if ($.browser.msie) {
	// no it doesn't

But things are rapidly changing. The latest version of IE is almost a modern browser, but as usual it’s making front end development a pain. Earlier versions of IE were generally as equally sucky as their predecessors, so it enabled lazy JavaScript developers to simply detect if (ie) and execute some proprietary Microsoft slops syntax. Now IE9 has done away with these functions, but that old if (ie) chestnut is throwing a spanner in the works.

So what if you could detect support for individual features without sniffing the (unreliable and cloakable) user-agent?

If you answered “that would be ghetto”, then you are correct.

In steps Modernizr, a JavaScript library developed in part by industry dream-boat Paul Irish. With wide adoption, tiny file-size and plenty of documentation: implementing it is a no-brainer. It creates a Modernizr object that contains the results of its detection tests, so checking feature support is as simple as the following:

// old way of detecting canvas support
if (!!document.createElement('canvas').getContext) { ... }

// with Modernizr
if (Modernizr.canvas) { ... }

Readable Milliseconds

A handy way of writing milliseconds in a readable format. Great for beginners, but mostly a gimmick.

// is this 3, 30 or 300 seconds?
var timeout = 30000; 

// an extra calculation, but easier to read and modify
var timeout = 30 * 1000;

jQuery Specific

Chain Like a Mad Dog

One of the best parts of jQuery is its function chaining. You’ve probably used it a bit, maybe a few simple calls one after another… but have you ever traversed the DOM like a mad dog? Take some time to familiarise yourself with the .end() function. It is critical for when you begin stepping up and down the DOM tree from your original selector.

	.find("a").text("Click here").bind("click",doStuff).end()

In the example above, the .end() function is used once we have finished doing things with a particular DOM object and want to traverse back up the DOM to the original object we called. We then load back up and dive back into the DOM.

Using data-* Attributes

Those of you who have been writing JavaScript (and not jQuery) for a good length of time are most likely familiar with attributes. Setting them. Getting them. Abusing rel and title instead…

So when isn’t HTML5 or jQuery coming the rescue? New specs allow the use of data- prefixes on HTML elements to indicate attributes which can hold data, and jQuery does an awesome job of converting the designated string into the correct JavaScript type. It’s a beautiful partnership. Let’s create a DIV with some data attributes.

<div id="test" data-is-bool="true" data-some-number="123"></div>

Now even though our values are wrapped in quotation marks, they won’t be handled as strings:

typeof $("#test").data("isBool"); // boolean

typeof $("#test").data("someNumber"); // number


It’s also important to notice the lower casing required to get these snippets to work. But if you’re a great front end developer, you will still want to camel case your data variables. Like many places in JavaScript, a preceding hyphen signifies camel casing of the next letter. The following camel casing of the HTML attribute does not work and the same JavaScript used above will return undefined.

Does not work 🙁

<div id="test" data-isBool="true" data-someNumber="123"></div>

Does work 🙂

<div id="test" data-is-bool="true" data-some-number="123"></div>

‘.stop()’ Collaborate & Listen

Binding jQuery animations to mouse events is a key part of modern web-based user interaction. It’s also something that you see done poorly on even the most famous of web sites. This article provides a straight forward example of built up animations and demonstrates how visually jarring they can be. Thankfully it’s easily fixed with a single function prefix or a parameter added to $.animate calls.

When using $.animatequeue: false can be added to the parameters to prevent chaining. Animation shortcuts such as$.fadeIn or $.slideDown do not take queue settings. Instead you have to pre-empt these animations with the $.stop method of pausing currently executing animations. Certain scenarios require the animation to stop dead in its tracks, or to jump to the end of the transition. It is recommended you familiarise yourself with the documentation of the parameters clearQueue andjumpToEnd, because god knows I can’t help you there.


	property: value
}, {
	duration: 1000,
	queue: false

Optimise Your Selectors

jQuery is pretty chill. It can do pretty much everything but make you coffee, and I hear that’s in the roadmap for 2.0. One thing you have to be careful about is abusing the power that is the sizzleJS selector engine. There are two strategies to overcome this: caching the selector results and using efficient selectors.


Do a costly DOM query every time you want to change something, or store a reference to the element? Pretty clear choice.

// before
$(".quote a").bind("click", doStuff); // DOM query eww

// now
$(".quote a").addClass("quoteLink"); // DOM query eww

// later
$(".quote a").fadeIn("slow"); // DOM query eww

Ignoring chaining, this is better:

// before
var $quoteLinks = $(".quote a");  // the only DOM query
$quoteLinks.bind("click", doStuff);

// now

// later


So jQuery/sizzleJS can use CSS3 selectors like a boss, but what’s the real cost? Behind the scenes the browser is hopefully using document.querySelector(), but there’s also a fair chance it will be breaking down your selector string and querying the DOM manually.

// an ID search is the quickest possible query, then it just takes a list of the childNodes and matches the class

// looks for the "foo" class only in the pre-defined bar element

A ‘for’ Loop is Always Quicker Than a ‘each()’ Loop

No matter what happens in the next few years of browser development, a native for loop will always be quicker than a jQuery$.each() loop. When you think of what jQuery really is (a library wrapped around native JS functions) you begin to realise that the native underlying JavaScript is always going to be quicker. It’s a tradeoff of run speed versus authoring speed.

It is vital that a native for loop is always used for performance critical functions that could fire potentially hundreds of times per second. Examples include:

  • Mouse movement
  • Timer intervals
  • Loops within loops


Understanding the Box Model is Key

The “box model” is a key determining factor in how a browser renders your page. A healthy understanding of it’s intricacies will make your job so indescribably easier. The box model denotes the way in which the physical dimensions of a HTML element are calculated. If a block element has a fixed width of say, 100px, then how should the padding, border and margin be placed?

Plenty of websites offer in depth descriptions, but put simply: the standards compliant implementation places the border and padding outside of the specified width. It’s best explained with a graphic. Consider this code:

/* the old way (178 + 20 + 2 = 200) */
.foo {
	width: 150px;
	height: 150px;
	padding: 25px;
	border: 25px solid;
	margin: 20px;


The padding and border are calucated inward, preserving the height and width specifically set to be 150px.

Box Model - Quirks Mode


Instead, you get 250px. 150px + (2 * 25) + (2 * 25).

Box Model - Standards Mode

If you think it seems odd, you’re not alone. There is a fix at hand, and it involves a CSS property called box-sizing, and it works in IE8 and above. It allows you to choose the exact way in which an elements dimensions are calculated, and its a lifesaver. Parameter support varies and vendor prefixes apply, so consult caniuse for specifics.

/* the old way (178 + 20 + 2 = 200) */
.foo {
	width: 178px;
	padding: 10px;
	border: 1px;

/* a better way */
.foo {
	width: 200px;
	padding: 10px;
	border: 1px;
		-webkit-box-sizing: border-box;
		-moz-box-sizing: border-box;
		box-sizing: border-box;

While it was always possible to mentally calculate widths by removing pixel units from each other (as per the first method), it was never entirely clear how to do so with variable width units like percentages and EMs. There was no other solution at this point besides wrapping elements in parent elements to ensure widths and padding/margin/borders could all be separate.

Know when to Float, and when to Position

Gone are the days of table based layouts. The moment we admit that we can concentrate our efforts into better understanding the way floats and positions work. There’s a particular mental model that needs to be grasped, and I believe this is something best done with practise.

Floats are great for sucking elements out of the DOM and forcing them hard up against a left or a right edge. They became the bread and butter of the post table layout stage in front end dev, possibly because of the poor browser support of display: inline and inline-block, as well as z-index bugs stemming from position support. These days there really is no excuse. Inline-block is fairly well supported, and a quick hack will get it working in IE7.

The arguments that previously held back absolutely positioning elements with CSS have thankfully died down. In theory, positioning allows you to place elements on a page (or within any container for that matter) with Xs and Ys in a straightforward manner that should be familiar to people like Flash developers.


It’s important to understand one fact when positioning elements with CSS: the position is always relative to the nearest positioned parent element. When people first start dabbling with CSS, there’s a common misconception that position: absolute; positions right up to the page root. I think this stems from the fact that, yes, without any parent elements with position styles – this is true. It traverses up the DOM tree, not finding any positioned elements, and settles on the root of the page.

So if position: absolute; pulls elements out of their normal flow, how do you position an element relative to it’s parent? That’s straight forward. The parent element needs to by styled position: relative;, and then all child elements will draw from the top, right, bottom and left of this parent container. Using this knowledge, how would you go about achieving the following straightforward layout?

How would go about coding up this image?

Using float, you would need to wrap the items in a clearfix, float .one left, and fiddle with floats and margins on both .twoand .three. You would end up with something similar to the following:

.parent {
	/* ghetto clearfix */
	width: 310px;
	overflow: auto;
.one {
	width: 200px;
	height: 210px;
	float: left;
.two {
	width: 100px;
	height: 100px;
	float: right;
	margin-bottom: 10px;
.three {
	width: 100px;
	height: 100px;
	float: right;

Using position allows us to, as described earlier, paint the elements on the screen with x and y co-ordinates in a very explicit way. While the above method with floats will break long lines down the page, the below method will keep everything in place, regardless of content.

.parent {
	position: relative;
	width: 310px;
	height: 210px;
.one, .two, .three {
	position: absolute;
.one {
	top: 0;
	left: 0;
	width: 200px;
	height: 210px;
.two {
	top: 0;
	right: 0;
	width: 100px;
	height: 100px;
.three {
	bottom: 0;
	right: 0;
	width: 100px;
	height: 100px;

As mentioned earlier, there are z-index issues to be considered. While the above example might seem a bit excessive, once you start thinking with positions, it will opens a world of possibilities.


Whitespacing of CSS can be difficult as we chop and change between single and multi line CSS arguments. I’m not going to get into that.


/* BAD */
.selector {display:none;background:#ff0000;color:#000000;} 

.selector { display: none; background: #ff0000; color: #000000; } 

.selector {
	display: none;
	background: #ff0000;
	color: #000000;


.selector {
	display: none;
	background: #ff0000;
	color: #000000;


Purely optional, and personally only employed when in a document with single line declarations.

.selector { display: none; background: #ff0000; color: #000000; }
	.selector a { text-decoration: none; }
	.selector span { font-weight: bold; }


.selector {
	background: #FFF; border: 1px solid #000; color: #EAEAEA;
		-webkit-border-radius: 3px;
		-moz-border-radius: 3px;
		border-radius: 3px;

CSS Shorthand


Grouping properties together is one of the single most effective methods to greatly reduce the size of a CSS file. It’s important to understand how properties are ordered (clockwise – top, right, bottom, left) and how they can be further shortened (top and bottom, left and right).

padding-top: 1px;
padding-right: 2px;
padding-bottom: 1px;
padding-left: 2px;

/* BETTER */
padding: 1px 2px 1px 2px;

/* BEST */
padding: 1px 2px;


Assigning a unit type to a property value of zero is redundant. It is not important to know whether an element should be 0pxfrom the left or 0 elephants from the left, just that it’s bang on the left.

/* BAD */
padding: 0px 10px;
/* GOOD */
padding: 0 10px;

Commenting Blocks

Commenting large blocks of CSS is a great way of keeping track of multiple style areas within the one stylesheet. Obviously it works better with single line CSS styles, but the effect is not entirely lost on multi-line either. The use of dashes versus equals versus underscores are all up the individual, but this is how I like to manage my stylesheets.

/* === HORIZONTAL NAV === */
#horizNav { width: 100%; display: block; }
#horizNav li { display: block; float: left; position: relative; }
#horizNav li a { display: block; height: 30px; text-decoration: none; }
#horizNav li ul { display: none; position: absolute; top: 30; left: 0; }

/* === HOME PAGE - CAROUSEL === */
#carousel { width: 960px; height: 150px; position: relative; }
#carousel img { display: none; }
#carousel .buttons { position: absolute; right: 10px; bottom: 10px; }

Clearing Floats

Clearing a <div> used to mean extra DOM, because it involved adding an extra clearer element. The better way is to set a specific width on the parent element (“auto” doesn’t work in all browsers and scenarios) and an overflow value of either “auto” or “hidden”. “Hidden” obviously degrades better, but there are some IE compatibility versions where “auto” works better.


<div class="parentElement">
	<div class="childElement">
		I'm floated left!
	I'm normal text that wraps around the float


.parentElement {
	width: 100%;
	overflow: hidden;
.childElement {
	float: left;

Contributors have also brought the latest clearfix to my attention. The micro clear-fix is considered stable and cross browser compliant enough to make it to the latest HTML5 boiler plate release. I highly recommend you check it out. Although I am not a massive fan of browser-specific CSS and pseudo elements such as :after, the micro clearfix is definitely more robust. It also prevents top margins from collapsing which is an absolute life saver.

Vertical & Horizontal Centering

Centering elements horizontally is not exactly rocket science, and I’m sure most of you are familiar with the following snippet:

.class {
	width: 960px;
	margin: 0 auto;

Front end devs have been using this snippet for a long time, without fully understanding why it didn’t work vertically. From my understanding, it’s important to remember that the parent element will generally have a height: auto; on it, and that there is no 100% height in which to vertically center the element. Applying the position: absolute; effectively moves the element out into position mode and responds to the pushing and pulling of auto margins and no specific location.

.exactMiddle {
	width: 100px;
	height: 100px;
	position: absolute;
	top: 0;
	right: 0;
	bottom: 0;
	left: 0;
	margin: auto;

The downsides of this method include its lack of support in IE6 and IE7, and the absence of a scroll bar if the browser is resized to be smaller than the centered object. There are more methods on this page (this is Method 4), but this is by far the best.

The vertical centering of text in an element is also straightforward. If the text is on a single line, like a horizontal navigation item, you can set the line-height to be that of the element’s physical height.

#horizNav li {
	height: 32px;
	line-height: 32px;

Feature Sniff, Don’t Browser Sniff

In the earlier discusison of JavaScript feature detection, applying properties if a browser is any version of IE is increasingly problematic. Man-of-steel Paul Irish pioneered the use of IE version sniffing to address this problem, but Modernizr has since come to the rescue. Modernizr places classes on the root <html> element specifying whether features are supported. Bleeding edge styles can then easily cascade from (or be removed from) these classes.

.my_elem {
   -webkit-box-shadow: 0 1px 2px rgba(0,0,0,0.25);
   -moz-box-shadow: 0 1px 2px rgba(0,0,0,0.25);
   box-shadow: 0 1px 2px rgba(0,0,0,0.25);

/* when box shadow isn't supported, use borders instead */
.no-boxshadow .my_elem {
   border: 1px solid #666;
   border-bottom-width: 2px;

You’re Not !important

A reliance upon the !important tag is a dangerous thing. The cases that warrant its use are rare and specific. They revolve around the necessity to override another stylesheet which you do not have access or permission to edit. Another scenario is hard coding an element’s styles to prevent inline JavaScript styles from taking precedence. Instead !important is used as a lazy shortcut to set the priority of your style over another, causing headaches further down the line.

The use of the !important tag can be mostly avoided via the better understanding of CSS selector precedence, and how to better target elements. The more specific the selector, the more likely it will be accepted as the applicable style. The following example from vanseodesign demonstrates the specificity at work.

p { font-size: 12px; } { font-size: 14px; }

Their article on style precedence does a better job explaining inheritence than I ever could, so please give it a go.

Aggressive Degradation

It’s worth noting that this is a personal opinion, and best suited to very specific situations. The stance of aggressive degradation will not be well received in large commercial projects or enterprise solutions relying upon older browsers.

Aggressive degradation dictates that if a particular (older) browser cannot render a certain effect, it should simply be omitted. A CSS3 button is a good example. Effects such as border-radiusbox-shadowtext-shadow and gradients will be displayed in cutting edge browsers. A graceful fallback of a .PNG would be provided for slightly older browsers, and the most graceful of all solutions would include a PNG-Fix for IE6 or the use of filter arguments to replicate gradients and shadows. However, aggressive degradation in this situation instructs you to neglect the older browsers and present them with a flat, satisfactory object.

Put simply, aggressive degradation boils down to: if your browser can’t render a gradient or a box shadow, tough luck.

While not ideal for every situation, it ensures the timely delivery of projects and that the root product is still usable and not reliant on (validation breaking) hacks.


Feature Sniff with Modernizr

I think I’ve gone on enough about this already. Use Modernizr to detect the availability of specific HTML5 and CSS3 features.

@font-face Use and Abuse

Before you consider embedding a custom font, is important that you inspect the EULA and check if web embedding is allowed. Foundries are understandably reluctant to allow designers and developers the ability to place font files directly on a server which can then be copied by a savvy end user. Particular foundries also prohibit the embedding of particular file types, such as.TTF and .OTF.

If, after careful consideration, you believe the desired font is web embeddable: head on over to the Font Squirrel @font-face Generator. It utilises Fontspring’s bulletproof @font-face structure and automatically generates all the required file formats.


Thankfully browser handling of unsupported HTML5 and CSS3 is already that of a graceful nature. New additions to the list of<input /> types such as “email”, “search” etc. will generally degrade to normal <input type="text" /> when not natively supported. Similarly, CSS3 properties that aren’t supported will simply not appear. Responsive layouts controlled by height and width media queries are simply not applied.

Subtle CSS3 effects should be employed as a reward for users who run a modern browser.

The resources section below includes a few libraries to help normalise HTML5 and CSS3 functionality across a range of older browsers.


Useful Resources

The following resources are vital for the standardisation of code and interaction in a modern web page. They ensure that CSS3 and HTML5 features are made accessible across a range of browsers that previously lacked support.

Support and Suggestions

This document was prepared by Tait Brown (@taitems).

Questions, corrections and suggestions can be lodged on the GitHub repository for this page. You can also fork your own branch and add your own company/product specific guidelines.