JavaScript Name and Coding Conventions.md

JavaScript Coding Conventions

Object Name	Notation	Length	Plural	Prefix	Suffix	Abbreviation	Char Mask	Underscores
Function name	camelCase	50	Yes	No	Yes	Yes	[A-z][0-9]	No
Function arguments	camelCase	50	Yes	No	No	Yes	[A-z][0-9]	No
Local variables	camelCase	50	Yes	No	No	Yes	[A-z][0-9]	No
Constants name	PascalCase	50	Yes	No	No	Yes	[A-z][0-9]	No
Field name	camelCase	50	Yes	No	No	Yes	[A-z][0-9]	No

Coding conventions are style guidelines for programming. They typically cover:

1. Naming and declaration rules for variables and functions.
2. Rules for the use of white space, indentation, and comments.

Coding conventions secure quality:

1. Improves code readability
2. Make code maintenance easier

Always use the same naming convention for all your code. For example:

1. Do use camelCasing for variables, function names and function argument names;
2. Do use PascalCasing for global variables;
3. Do use UPPERCASE for constants (like PI);
4. Do not use under_scores in variable, constants, function arguments or function names;
5. Do not use hyphens in JavaScript names.

Naming Conventions

Do use camelCasing for function names:

function helloWorld()	
{
}

Do use camelCasing for function arguments and local variables:

function hello(isShow)	
{
}

firstName = "John";
lastName = "Doe";

price = 19.90;
discount = 0.10;

fullPrice = price * 100 / discount;

Note: Don't start names with a $ sign. It will put you in conflict with many JavaScript library names.

Spaces Around Operators

Always put spaces around operators ( = + / * ), and after commas:

Examples:

var x = y + z;
var values = ["Volvo", "Saab", "Fiat"];

Code Indentation

Always use 4 spaces for indentation of code blocks:

Functions:

function ToCelsius(fahrenheit) {
    return (5/9) * (fahrenheit-32);
}

Note: Do not use tabs (tabulators) for indentation. Text editors interpret tabs differently.

Statement Rules

General rules for simple statements: Always end simple statement with a semicolon.

Examples:

var values = ["Volvo", "Saab", "Fiat"];

var person = {
    firstName: "John",
    lastName: "Doe",
    age: 50,
    eyeColor: "blue"
};

General rules for complex (compound) statements:

1. Put the opening bracket at the end of the first line.
2. Use one space before the opening bracket.
3. Put the closing bracket on a new line, without leading spaces.
4. Do not end complex statement with a semicolon.

Functions:

function toCelsius(fahrenheit) {
    return (5/9) * (fahrenheit-32);
}

Loops:

for (i = 0; i < 5; i++) {
    x += i;
}

Conditionals:

if (time < 20) {
    greeting = "Good day";
} else {
    greeting = "Good evening";
}

Object Rules

General rules for object definitions:

1. Place the opening bracket on the same line as the object name.
2. Use colon plus one space between each property and its value.
3. Use quotes around string values, not around numeric values.
4. Do not add a comma after the last property-value pair.
5. Place the closing bracket, on a new line, without leading spaces.
6. Always end an object definition with a semicolon.

Example:

var person = {
    firstName: "John",
    lastName: "Doe",
    age: 50,
    eyeColor: "blue"
};

Short objects can be written compressed, on one line, like this:

var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

Line Length < 80

For readability, avoid lines longer than 80 characters. If a JavaScript statement does not fit on one line, the best place to break it, is after an operator or a comma.

Example:

document.getElementById("demo").innerHTML = "Hello World.";

Loading JavaScript in HTML

Use simple syntax for loading external scripts (the type attribute is not necessary):

<script src="myscript.js">

Accessing HTML Elements

A consequence of using "untidy" HTML styles, might result in JavaScript errors. These two JavaScript statements will produce different results:

var obj = getElementById("Demo")
var obj = getElementById("demo")

If possible, use it naming convention (as JavaScript) in HTML.

File Extensions

1. HTML files should have a .html extension (not .htm);
2. CSS files should have a .css extension;
3. JavaScript files should have a .js extension.

Official Reference

1. Google JavaScript Style Guide
2. JavaScript Style Guide and Coding Conventions