JavaScript Style Guide and Coding Conventions

Always use the same coding conventions for all your JavaScript projects.

JavaScript Coding Conventions


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

Coding conventions secure quality:

Coding conventions can be documented rules for teams to follow, or just be your individual coding practice.

This page describes the general JavaScript code conventions used by NGO. You should also read the next chapter "Best Practices", and learn how to avoid coding pitfalls.

Variable Names


At NGO we use camelCase for identifier names (variables and functions).

All names start with a letter.

At the bottom of this page, you will find a wider discussion about naming rules.

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

price = 19.90;
tax = 0.20;

fullPrice = price + (price * tax);

Spaces Around Operators


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


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

Code Indentation


Always use 4 spaces for indentation of code blocks:


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

Do not use tabs (tabulators) for indentation. Different editors interpret tabs differently.

Statement Rules


General rules for simple statements:


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

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

General rules for complex (compound) statements:


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


for (i = 0; i < 5; i++) {
    x += i;


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

Object Rules


General rules for object definitions:


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

Short objects can be written compressed, on one line, using spaces only between properties, 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.


document.getElementById("demo").innerHTML =
    "Hello Dolly.";
Try it Yourself

Naming Conventions


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

Should you use hyp-hens, camelCase, or under_scores in variable names?

This is a question programmers often discuss. The answer depends on who you ask:

Hyphens in HTML and CSS:

HTML5 attributes can start with data- (data-quantity, data-price).

CSS uses hyphens in property-names (font-size).

Hyphens can be mistaken as subtraction attempts. Hyphens are not allowed in JavaScript names.


Many programmers prefer to use underscores (date_of_birth), especially in SQL databases.

Underscores are often used in PHP documentation.


PascalCase is often preferred by C programmers.


camelCase is used by JavaScript itself, by jQuery, and other JavaScript libraries.

Do not start names with a $ sign. It will put you in conflict with many JavaScript library names.

Loading JavaScript in HTML


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

<script src="myscript.js"></script>

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 the same naming convention (as JavaScript) in HTML.

File Extensions


HTML files should have a .html extension (not .htm).

CSS files should have a .css extension.

JavaScript files should have a .js extension.

Use Lower Case File Names


Most web servers (Apache, Unix) are case sensitive about file names:

london.jpg cannot be accessed as London.jpg.

Other web servers (Microsoft, IIS) are not case sensitive:

london.jpg can be accessed as London.jpg or london.jpg.

If you use a mix of upper and lower case, you have to be extremely consistent.

If you move from a case insensitive, to a case sensitive server, even small errors can break your web site.

To avoid these problems, always use lower case file names (if possible).



Coding conventions are not used by computers. Most rules have little impact on the execution of programs.

Indentation and extra spaces are not significant in small scripts.

For code in development, readability should be preferred. Larger production scripts should be minified.