Javascript Code Style Guide with examples

1.Variables, functions, properties methods:

// Good
var thisIsMyName;
var anotherVariable;
var aVeryLongVariableName;

Methods:
// Good
function getName() {
return myName;
}

// Bad: Easily confused with variable
function theName() {
return myName;
}


Constants:

// Good
eg:
// Changing this value will be problem
var MAX_COUNT = 10;

var URL = "http://www.mydomain.net/";
if (count < MAX_COUNT) {
doSomething();
}

Global References:
 // Note: Specify about below declaration,where they are used
 var globalPreferedMode = false;
 var globalUserPreferenceArr = [];  // Array used to compare with preference cols of trade grid while applying preferences


2. Single line comments:
eg:
// Good
if (condition) {

// if you made it here, then all security checks passed
allowed();
}

eg:
// Good
var result = something + somethingElse; // somethingElse will never be null

Multiline comments:
eg:
// Good
if (condition) {
/*
* if you made it here,
* then all security checks passed
*/
allowed();
}

eg:
// Bad: Don't use multiline comments for trailing comments
var result = something + somethingElse; /*somethingElse will never be null*/


3. Constructors:

// Good
function Person(name) {
this.name = name;
}
Person.prototype.sayName = function() {
alert(this.name);
};
var me = new Person("Raja");


4. Literal Values:

// Valid JavaScript
var name = "Sencha says, \"Hi.\"";

// Also valid JavaScript
var name = 'Sencha says, "Hi"';

// Good
var longString = "Here's the story, of a man " +
"named Brady.";

Numbers:

// Integer
var count = 10;
// Decimal
var price = 10.0;
var price = 10.00;


5.using NULL?

// Good
var person = null;

// Good
function getPerson() {
if (condition) {
return new Person("Sencha");
} else {
return null;
}
}

// Good
var person = getPerson();
if (person !== null) {
doSomething();
}

// Bad: Testing against uninitialized variable
var person;
if (person != null) {
doSomething();
}
// Bad: Testing to see whether an argument was passed
function doSomething(arg1, arg2, arg3, arg4) {
if (arg4 != null) {
doSomethingElse();
}
}


6. Using Undefined:

// Bad
var person;
console.log(person === undefined); //true

// foo is not declared
var person;
console.log(typeof person); //"undefined"
console.log(typeof foo); //"undefined"

// Good
var person = null;
console.log(person === null); //true


7. Object Literals:

// Bad
var book = new Object();
book.title = "Maintainable Sencha Code";
book.author = "Sencha EXTJS";


// Good
var book = {
title: "Maintainable Sencha Code",
author: "Sencha"
};

8. Array Literals:

// Bad
var colors = new Array("red", "green", "blue");
var numbers = new Array(1, 2, 3, 4);

// Good
var colors = [ "red", "green", "blue" ];
var numbers = [ 1, 2, 3, 4 ];

9.Line Length
Line length is less frequently found in JavaScript style guidelines, but Crockford’s Code
Conventions specifies a line length of 80 characters. I also prefer to keep line length at 80 characters.

10. Equality
Equality in JavaScript is tricky due to type coercion.

Use of === and !== is recommended by Crockford’s Code Conventions
// Null and undefined
console.log(null == undefined); // true
console.log(null === undefined);// false

// The number 5 and string 5
console.log(5 == "5"); // true
console.log(5 === "5"); // false

11. Primitive Wrapper Types
There are three primitive wrapper types: String, Boolean,
and Number. Each of these types exists as a constructor in the global scope and each
represents the object form of its respective primitive type. The main use of primitive
wrapper types is to make primitive values act like objects, for instance:

// Bad
var name = new String("Raja");
var author = new Boolean(true);
var count = new Number(10);