JavaScript Best Practices

JavaScript is not only amazing language but also very tricky language. To make correct use of it, you need to follow some best practices to avoid any problems that might come about otherwise. I share some of the best practices you really should be following when writing JavaScript code. Of course this is not an exhaustive list but at the most fundamental level, every programmer should know and adhere to it.

1 -NEVER FORGET VAR KEYWORD

Most of the developers know about this but yet I wanted to mention this because it may not be clear to some or newbies or people having other programming language background that come to JavaScript.

Consider the following piece of code:

function myFunc(){
var firstName = 'sarfraz';
lastName = 'ahmed';
}

It should be noted that in JS, variables have function-level scope which means a variable declared inside a function can not be accessed outside of it. So let's test above two variables:

myFunc();
console.log(lastName); // ahmed
console.log(firstName); // undefined

As you will notice, we are still able to access lastName variable. The reason is that it does not have function-level scope because we forgot to put var keyword before it unlike firstName variable. Hence, lastName variable went into global scope and became part of window (while inside browser) object eg window.lastName will output the last name too.

It is therefore always required to put var keyword before variables so that they do not become part of global scope. It has following benefits:

  • You save the memory and improve performance
  • You don't pollute the global scope
  • You mistakenly don't overwrite a global variable that might have the same variable name

This is a very important concept and JS developers have always been finding solutions to avoid this problem. One of the most popular solution is Singleton or Module Pattern you should check out. By the way, if you want to see other patterns also, take a look at:

Essential JavaScript Design Patterns For Beginners

2 - DECLARE VARIABLES ON TOP

Another thing that should be followed is that variables should be declared on top of each function because of what is known as JavaScript Hoisting. Here is an example:

var name = 'sarfraz';

(function(){
console.log(name); // undefined
     var name = 'nawaz';
     console.log(name); // nawaz
})();

Notice that even though name variable is outside the scope of function but on the very fist line it gives back undefined rather than actual name. The reason for this is that interpreter hoists or moves variables on top of the function, here is how interpreter sees or re-arranges it:

var name = 'sarfraz';

(function(){
     var name;
     console.log(name); // undefined
     name = 'nawaz';
     console.log(name); // nawaz
})();

As can be seen, name variable has been hoisted to top and declared there and also var keyword has been stripped from it where we assigned the value of 'nawaz'.

The same is issue is not only with variables but also function declarations but NOT with function expressions. You can learn more about the difference between function declaration and function expression here:

Named Functions Demystified

The solution to this problem is to always declare variables and function declarations on top of container function:

function myFunc(){
     var foo;
     var bar;
     var baz;

     // do something foo, bar, baz
}

The preferred and recommended syntax though that you must follow is to declare all variables in one go by separating them with a comma:

function myFunc(){
     var foo, bar, baz;

     // do something foo, bar, baz
}

3 - INITIALIZING MULTIPLE VARIABLES

Declaring variables on top is good practice but not multiple initialization. Consider:

function myFunc(){
var lang = encoding = 'en';
}

This is a very common mistake even amongst experienced JS developers where they think they have quickly assigned two variables same scope and same value. Though value for both lang and encoding variable is some but not the scope. Try it out:

myFunc();
console.log(encoding); // en
console.log(lang); // undefined

Here again, variable encoding has gone into global scope. Since var keyword is only appears before lang variable, that is the one which gets correct functional scope. In short, you should avoid that shorthand initialization unfortunately.

4 - STARTING CURLY BRACE ON THE SAME LINE

Consider the following code block where starting curly brace "{" is on a new line, this works fine in most situations.

function myFunc()
{
// some code
}

However, same convention will not yield expected results if you happen to write:

function myFunc()
{
     return
     {
         name: 'sarfraz'
     };
}

var f = myFunc();
console.log(f);

The result will be undefined because behind the scenes, interpreter puts a semicolon ';' after the return keyword making it:

function myFunc()
{
     return; // <----------------
     {
         name: 'sarfraz'
     };
}

To remedy such hard-to-debug issues, it is good practice to always put starting curly brace on the same line, this would work fine though:

function myFunc() {
     return {
         name: 'sarfraz'
     };
}

var f = myFunc();
console.log(f.name); // sarfraz

And that's a reason why Douglas Crockford in his book "JavaScript: The Good Parts", advocates this syntax for JS:

function () {
     // some code
}

if (expression) {
     // do something
}

Go ahead and check out JavaScript Coding Style to learn more as well as naming conventions.

Notice that it is not the return keyword affected by automatic semi-colon insertion but all these too:

  • var statement
  • empty statement
  • expression statement
  • do-while statement
  • continue statement
  • break statement
  • throw statement

Experienced JavaScript developers know pretty well about JavaScript's automatic semi-colon insertion problem and avoid it. The benefit of above coding style however is that you avoid this problem without knowing that this problem exists just by following that coding style.

5 - USE ARRAY LITERAL INSTEAD OF NEW ARRAY()

There are two ways you can create arrays in JS:

var arr1 = new Array(); // array constructor
var arr2 = []; // array literal

Though both serve the purpose of creating arrays but there is important difference between the two.

In JS, even an array is an object. With first constructor method above, you are telling interpreter to call constructor of the Array and generate an object. The interpreter looks up into the execution context to find the constructor and once found, it calls it and creates the Array object. It seems that it has performance hit too as compared to latter array literal method. With the array literal method, interpreter just creates the array on run-time with no extra processing done.

Other than that, Array constructor is mis-guiding the way it handles its parameters. Consider:

console.log(new Array(5)); // [,,,,]
console.log(new Array('5')); // ["5"]

When one argument is passed to Array and that happens to be a number, a new array is returned with its length property equal to that number passed. The important thing to note here is that Array will be initialized from what number you specified to it, for example:

// Array constructor
var arr = new Array(2);
console.log(arr.length); // 2
console.log(arr[0]); // undefined

// Array literal
var arr = [2];
console.log(arr.length); // 1
console.log(arr[0]); // 2

So the conclusion is to always use array literal notation rather than Array constructor.

6 - USE PROTOTYPE TO SHARE ACROSS

The concept of prototypes or prototypal inheritance is rather confusing. I have seen people especially inexperienced JS developers adding class members to parent function which needs to be shared across child classes. Consider the following code:

function Person(name){
this.name = name;
}

Now let's assume we want to have child classes the ability to display the names some how, one of doing it is putting method directly inside Person class:

function Person(name){
     this.name = name;

     this.display = function(){
         alert(this.name);
     }
}

Other way is to use prototype:

function Person(name){
     this.name = name;
}

Person.prototype.display = function(){
     alert(this.name);
}

With both ways, all child classes will be able to use the display method but there is important difference between the two. When you attach any methods or properties via this (first way above) to a class then all instances of inheriting child classes will also have these properties or methods within them or their signature. On the other hand, when you use prototype to add members (properties and methods) to parent class, children classes will still inherit all members but it won't be present inside their own functionality or signature, rather they will be borrowing that functionality from their parent class thereby saving memory. For this reason, later approach seems good to follow in most situations.

7 - PUT COMMA BEFORE PROPERTIES

When working with objects or arrays, it is always a good idea to put a comma before the variable or object property eg:

// jQuery - create a new div with some css
$('</pre></pre></pre>
<div>').attr({</div>
<pre>
<pre>
<pre>
 "id" : "myId"
 , "class" : "myClass"
 , "class" : "myClass"
 , "color" : "green"
 , "fontWeight" : "bold"
});

In this way, we never add an extra comma or forget one from the last property. The reason why this is good practice is that, in IE, with extra comma at the last property, we do not get expected results sometimes (ExtJS developers must have learned this). I do the same with multiple variable declarations or arguments of function. It also makes the code look pretty too as far as I see it.

8 - DON'T MIX JS AND HTML

One of the most important best practices is to always separate JS code from HTML and go unobtrusive. One would often see code like this:

<a href="#" onclick="doSomething()">Some Action</a>
<input type="button" onclick="doSomething()" value="Do Something" />
<form onsubmit="doSomething();">...

That's a very bad practice in that it is hard to manage and maintain. HTML and JS should not be mixed ever. You could do the same thing like this:

<a href="#" id="link">Some Action</a>
<input type="button" id="button" value="Do Something" />
<form id="frm">...

<script type="text/javascript">
var link = document.getElementById('link'),
 btn = document.getElementById('button'),
 frm = document.getElementById('link');

link.onclick = function(){
 // do something
};

btn.onclick = function(){
 // do something
};

frm.onsubmit = function(){
 // validate form
};

</script>

This way it becomes easy to manage, maintain or enhance both HTML and JavaScript.

9 - PUT SCRIPTS AT BOTTOM

Normally scripts are put in <head></head> tags but this should be avoided. The reason for this is that browser loads your scripts sequentially and by the time they are loading, nothing else is done and website load times slow down (or at least that's how visitors will perceive it) and you see actual output only after those scripts have been loaded by the browser.

The best practice is that scripts should be put on bottom of page just before closing body tag eg </body>. This way browser will instantly display page and page load time will be better for users who view that page.

By the way, always put CSS on top in <head></head> tags because that's something browser reads first and renders page's layout accordingly.

Read more about this at famous Yahoo's performance article.

I would also suggest you to use Yahoo's YSlow or Google's PageSpeed add-on (add-ons of Firebug) which suggest you a lot of things on how to improve the performance of the page.

10 - NEVER FORGET SEMI-COLON

Always end statements and function expressions with a semi-colon:

var name = 'some name'; // <-------------

var myFunc = function(){
// some doe

}; // <------------

This is useful when you want to compress the code (for faster load times). If at any place, semi-colon isn't present, you won't be able to compress the code or wouldn't get expected results most likely code-wise. You should always, always use semi-colons.

BONUS

The good news is that you can solve most of above problems by using JSHint or JSLint code quality tool. It will tell you about best-practices and any errors that might exist in your code. Having said that, it is good to improve your JS skills and avoid the need to go to such tools.

Introducing WebNote Chrome Extension

I like to read and research and as such I always bookmark interesting articles both locally and online eg Google Bookmarks or some other service. Since we do not always have the time to read an article of our interest the time we come across it, we use online bookmarking services to save and read them later and that’s good.

However, I was looking for a solution which could allow me to save those articles locally on my computer and read them any time later, this is something useful in cases when you are not connected to internet and yet want to be able to have the access to articles you like. I came across Evernote which is pretty cool services you can use to save webpages, videos, voice and a lot more. My primary focus though was to save webpages/articles related to web development. Any page you save to Evernote (via their Web Clipper browser plugin), can be downloaded to your computer via Sync option of that software which is exactly what I was looking for. After using it for a while, it turned out that with FREE account only 60MB is allocated which I consumed within 15 days :(

As a developer, I thought of creating my own solution that could be used to save articles/pages locally rather than buying Evernote. So I went on to creating the Chrome extension named WebNote.

WebNote can be used to save webpages with all their content, images, css, etc locally. WebNote will prove useful for anyone who does research on a particular topic or reads a lot.

How It Works

Once extension is installed and you press its icon on the browser toolbar, it pops up with a window (screenshot below) which pre-fills the URL and Title of the page, allows you to select Folder you want to save the page in along with any optional Comments. The extension pre-fills folders field by reading them from the local database which means for the WebNote to work, you need to have WAMP setup locally. Once you press the Save button, the page’s information is saved in the very database. The page itself is saved on hard disk (folder where WebNote CMS will be installed) in MHT format and if you don’t know about MHT format, it is basically a format which saves all resources of a page including images, css in one single page. Internet Explorer supports this format which means saved pages will open in IE.

I won’t go into details of how I created Chrome extension (there are a lot of resources out there) or how pages are saved in MHT format with all their resources in single page or even the small CMS used to manage the pages saved via WebNote because everything can be downloaded (see Installation guide below) and source code can be viewed.

WebNote Screenshot


All the pages saved are accessed via little CMS that I wrote, here are some screenshots.

CMS Screenshots


Notice that from programming perspective, CMS’s code is ugly in that it does not separate PHP and HTML and CMS password is saved with no encryption (since it will run locally). There are some reasons behind that though:

  • I wanted to write application real quick – too lazy to separate php, html logic
  • It was only meant to be for personal use but today I decided to share it
  • It wasn’t meant to be a professional project in which I take all sorts of care

Anyways, it serves the purpose but you can still go ahead and modify the code however you like.

Installation

Installing Chrome Extension:

  • Download WebNote Chrome extension and extract contents somewhere
  • In Chrome, type “chrome://extensions/” (without quotes) in address bar, Extensions window will open
  • On the right side of Chrome Extension page, there will be a link “Developer mode“, click on that
  • Now click on the button “Load unpacked extension” and specify path where you extracted the WebNote extension
  • You will notice that a Notepad-like icon will be added to Chrome toolbar that is extension is installed

Installing CMS:

  • Download WebNote CMS and extract it in www/root folder of your WAMP installation folder
  • Open PHPMyAdmin or any other MySQL client of your choice and create a database named “webnote” (without quotes)
  • Import the sql file “webnote.sql” present in WebNote CMS folder in that newly created database
  • In the Webnote CMS folder, go to admin/includes/db.php and edit your database settings accordingly
  • Browse the CMS where you installed it in the browser like “http://localhost/foldername/admin“. You should see Admin login panel
  • Enter “admin” as username and “123123” as password without quotes.

Using WebNote

  • Once logged in, create some folders. You should see Add Folder link to the right of Navigation on the My Folders page.
  • To save a page, click the WebNote icon in the browser toolbar and hit the Save Now button
  • You will see ajax loading image, wait until page is saved. A notification will appear telling you that page is saved.
  • Go back to Admin panel, click on “My Folders” link and then click on the folder you saved the page in.
  • Click on the link title and it will open in Internet Explorer (because MHT is supported by it).

Notes & Tips

  • When you create a folder, it does not create a folder physically on your hard disk. Consider it kind of tag for each page.
  • All files are saved in “mht” folder inside CMS.
  • All other page information including title, folder, url, html is saved in database
  • To save pages, you obviously need to have internet connection to be able to save them locally and read them later
  • You can pre-populate “Comments” field by selecting some text on page and then hitting the WebNote icon in toolbar.

Have fun with your readings and research :)

Learning Javascript

JavaScript is cross-platform, cross-browser language; javascript is everywhere; web, RIA (rich internet applications), mobile, tablets, animations and even on server with the advent of node.js. Javascript is the language of the future.

I started off with jQuery without knowing anything much about javascript because by the time I didn’t find any reason to learn it due to fact that  javascript libraries did everything we needed putting complexities out of the way. Today I realize that I chose the wrong path, a good understanding of javascript language is crucial if you look at the reasons I have mentioned in the very beginning but it is never too late to start again, that’s exactly what I have decided, learning javascript seriously. I am not the only one who has started realizing the power and future of javascript, there are giants who have started learning it too. If you are also javascript-library-only developer, or even copy-paster programmer, you should really learn javascript !

Despite design flaws and bad reputation of the language as they say and probably rightly so, javascript is popular and language of the choice for those who have gone into deeper understating of it. Javascript language does have bad parts but its good parts over-weigh its bad parts and there is always room to avoid bad parts if you know the language right and use it effectively.

Javascript turns out to be extremely tricky language, consider:

// Comparison
'' == '0';    //false
0 == '';    // true
0 =='0';    // true

// Type checking
typeof null;    // object

// Scope
function myFunc() {
  return
  {
    name: 'sarfraz'
  };
}

var f = myFunc();
console.log(f);    // undefined

I did a lot of research to find best javascript learning resources. On the journey of my exploration, I came across some of the great resources with a lot of reviews and user feedback. By now, if you made your mind to take javascript seriously, here are the best resources out there you should check out.

Books

Online

Videos

Blogs to Subscribe

Tools

Let's start... :)