This guide outlines basic style rules and suggestions for writing JS in DataMade projects.
DataMade forked and customized the popular Node.js style guide, created by Felix Geisendörfer and licensed under the CC BY-SA 3.0 license.
There is a .jshintrc which enforces these rules as closely as possible. You can either use that and adjust it, or use this script to make your own.
- 4 Spaces for indentation
- Newlines
- No trailing whitespace
- Use semicolons most of the time
- 80 characters per line
- Use single or double quotes
- Opening braces go on the same line
- Declare one variable per var statement
- Use lowerCamelCase or snake_case for variables, properties, and function names
- Use UpperCamelCase for class names
- Use UPPERCASE for Constants
- Write small functions
- Return early from functions
- Name your closures
- No nested closures
- Method chaining
- Object.freeze, Object.preventExtensions, Object.seal, with, eval
- Requires At Top
- Getters and setters
- Do not extend built-in prototypes
You may want to use editorconfig.org to enforce the formatting settings in your editor. Use the Node.js Style Guide .editorconfig file to have indentation, newslines and whitespace behavior automatically set to the rules set up below.
Use 4 spaces for indenting your code and swear an oath to never mix tabs and spaces - a special kind of hell is awaiting you otherwise.
Use UNIX-style newlines (\n), and a newline character as the last character
of a file. Windows-style newlines (\r\n) are forbidden inside any repository.
Just like you brush your teeth after every meal, you clean up any trailing whitespace in your JS files before committing. Otherwise the rotten smell of careless neglect will eventually drive away contributors and/or co-workers.
According to scientific research, the usage of semicolons is a core value of our community. Consider the points of the opposition, but be a traditionalist when it comes to abusing error correction mechanisms for cheap syntactic pleasures.
Do not, however, use semicolons at the end of function declarations. They do not harm the code, but they do evaluate as an empty statement and provide zero value.
Right:
function feedSeymour(sandwich) {
return sandwich;
}Wrong:
function feedSeymour(sandwich) {
return sandwich;
};Limit your lines to 80 characters. Yes, screens have gotten much bigger over the last few years, but your brain has not. Use the additional room for split screen, your editor supports that, right?
You may use single or double quotes - but be consistent throughout your code. Use double quotes for JSON.
Right:
var foo = 'bar';
var bar = 'foo';Wrong:
var foo = "bar";
var bar = 'foo';Your opening braces go on the same line as the statement.
Right:
if (true) {
console.log('winning');
}Wrong:
if (true)
{
console.log('losing');
}Also, notice the use of whitespace before and after the condition statement.
Declare one variable per var statement, it makes it easier to re-order the lines. However, ignore Crockford when it comes to declaring variables deeper inside a function, just put the declarations wherever they make sense.
Right:
var keys = ['foo', 'bar'];
var values = [23, 42];
var object = {};
while (keys.length) {
var key = keys.pop();
object[key] = values.pop();
}Wrong:
var keys = ['foo', 'bar'],
values = [23, 42],
object = {},
key;
while (keys.length) {
key = keys.pop();
object[key] = values.pop();
}Variables, properties, and function names may use lowerCamelCase or snake_case. However, try to be consistent throughout the project. Names should also be descriptive. Single character variables and uncommon abbreviations should generally be avoided.
Note: CSS classes and ids usually contain hyphens, and functions borrowed from third-party libraries (e.g., fadeOut) might employ lowerCamelCase. No worries! Such inconsistently is inevitable: just be consistent within your own code.
Looks good:
function hideHelper() {
if(clickedBar==false){
$("#helper-occupation").fadeOut(700)
};
}function hide_helper() {
if(clicked_bar==false){
$("#helper-occupation").fadeOut(700)
};
}Not great:
function hideHelper() {
if(clicked_bar==false){
$("#helper-occupation").fadeOut(700)
};
}Class names should be capitalized using UpperCamelCase.
Right:
function BankAccount() {
}Wrong:
function bank_Account() {
}Constants should be declared as regular variables or static class properties, using all uppercase letters.
Right:
var SECOND = 1 * 1000;
function File() {
}
File.FULL_PERMISSIONS = 0777;Wrong:
const SECOND = 1 * 1000;
function File() {
}
File.fullPermissions = 0777;Use trailing commas and put short declarations on a single line. Only quote keys when your interpreter complains:
Right:
var a = ['hello', 'world'];
var b = {
good: 'code',
'is generally': 'pretty',
};Wrong:
var a = [
'hello', 'world'
];
var b = {"good": 'code'
, is generally: 'pretty'
};Programming is not about remembering stupid rules. Use the triple equality operator as it will work just as expected.
Right:
var a = 0;
if (a !== '') {
console.log('winning');
}Wrong:
var a = 0;
if (a == '') {
console.log('losing');
}Use the ternary operator only when it presents straightforward conditional results. If you need to split your code into multiple lines, use if and else wrappers instead. What would a ninja do?
Right:
var myTruthiness = (text != null) ? True : FalseWrong:
var myTruthiness = (text != null) && (text != '') && (text != 'gerbils')
? truthArray.push(text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'))
: truthArray.splice(0, 1)
.push('hamsters')
.reverse()Any non-trivial conditions should be assigned to a descriptively named variable or function:
Right:
var isValidPassword = password.length >= 4 && /^(?=.*\d).{4,}$/.test(password);
if (isValidPassword) {
console.log('winning');
}Wrong:
if (password.length >= 4 && /^(?=.*\d).{4,}$/.test(password)) {
console.log('losing');
}Keep your functions short. A good function fits on a slide that the people in the last row of a big room can comfortably read. So don't count on them having perfect vision and limit yourself to ~15 lines of code per function.
To avoid deep nesting of if-statements, always return a function's value as early as possible.
Right:
function isPercentage(val) {
if (val < 0) {
return false;
}
if (val > 100) {
return false;
}
return true;
}Wrong:
function isPercentage(val) {
if (val >= 0) {
if (val < 100) {
return true;
} else {
return false;
}
} else {
return false;
}
}Or for this particular example it may also be fine to shorten things even further:
function isPercentage(val) {
var isInRange = (val >= 0 && val <= 100);
return isInRange;
}Feel free to give your closures a name. It shows that you care about them, and will produce better stack traces, heap and cpu profiles.
Right:
req.on('end', function onEnd() {
console.log('winning');
});Wrong:
req.on('end', function() {
console.log('losing');
});Use closures, but don't nest them. Otherwise your code will become a mess.
Right:
setTimeout(function() {
client.connect(afterConnect);
}, 1000);
function afterConnect() {
console.log('winning');
}Wrong:
setTimeout(function() {
client.connect(function() {
console.log('losing');
});
}, 1000);One method per line should be used if you want to chain methods.
You should also indent these methods so it's easier to tell they are part of the same chain.
Right:
User
.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});Wrong:
User
.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' })
.populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec(function(err, user) {
return true;
});
User.findOne({ name: 'foo' }).populate('bar')
.exec(function(err, user) {
return true;
});Use slashes for both single line and multi line comments. Try to write comments that explain higher level mechanisms or clarify difficult segments of your code. Don't use comments to restate trivial things.
Right:
// 'ID_SOMETHING=VALUE' -> ['ID_SOMETHING=VALUE', 'SOMETHING', 'VALUE']
var matches = item.match(/ID_([^\n]+)=([^\n]+)/));
// This function has a nasty side effect where a failure to increment a
// redis counter used for statistics will cause an exception. This needs
// to be fixed in a later iteration.
function loadUser(id, cb) {
// ...
}
var isSessionValid = (session.expires < Date.now());
if (isSessionValid) {
// ...
}Wrong:
// Execute a regex
var matches = item.match(/ID_([^\n]+)=([^\n]+)/);
// Usage: loadUser(5, function() { ... })
function loadUser(id, cb) {
// ...
}
// Check if the session is valid
var isSessionValid = (session.expires < Date.now());
// If the session is valid
if (isSessionValid) {
// ...
}It is possible to use Django context variables in JavaScript. Cast these as strings within the JS.
Right:
var my_value = '{{ my_value }}';Wrong:
var my_value = {{ my_value }};Avoid calling standard Django or custom-built filters on the client-side. If you need to transform a value for use in JS, then do that transformation in the Django view.
Right:
var my_value = '{{ my_value_transformed }}';Wrong:
var my_value = {{ my_value|custom_filter }};Crazy shit that you will probably never need. Stay away from it.
Always put requires at top of file to clearly illustrate a file's dependencies. Besides giving an overview for others at a quick glance of dependencies and possible memory impact, it allows one to determine if they need a package.json file should they choose to use the file elsewhere.
Do not use setters, they cause more problems for people who try to use your software than they can solve.
Feel free to use getters that are free from side effects, like providing a length property for a collection class.
Do not extend the prototype of native JavaScript objects. Your future self will be forever grateful.
Right:
var a = [];
if (!a.length) {
console.log('winning');
}Wrong:
Array.prototype.empty = function() {
return !this.length;
}
var a = [];
if (a.empty()) {
console.log('losing');
}