These are numbers (or other values) simply used in line in your code. **Do not use these**, give them a variable name so they can be understood and changed easily.
*Right:*
```js
var minWidth = 300;
if (width <minWidth){
...
}
```
*Wrong:*
```js
if (width <300){
...
}
```
## Global definitions
Don't do this. Everything should be wrapped in a module that can be depended on by other modules. Even things as simple as a single value should be a module.
## Function definitions
Prefer the use of function declarations over function expressions. Function expressions are allowed, but should usually be avoided.
Also, keep function definitions above other code instead of relying on function hoising.
## Only use ternary operators for small, simple code
And **never** use multiple ternaries together
*Right:*
```js
var foo = (a === b) ? 1 : 2;
```
*Wrong:*
```js
var foo = (a === b) ? 1 : (a === c) ? 2 : 3;
```
## Do not extend built-in prototypes
Do not extend the prototype of native JavaScript objects. Your future self will
be forever grateful.
*Right:*
```js
var a = [];
if (!a.length) {
console.log('winning');
}
```
*Wrong:*
```js
Array.prototype.empty = function() {
return !this.length;
}
var a = [];
if (a.empty()) {
console.log('losing');
}
```
## Use descriptive conditions
Any non-trivial conditions should be assigned to a descriptively named variables, broken into
several names variables, or converted to be a function:
*Right:*
```js
var thing = ...;
var isShape = thing instanceof Shape;
var notSquare = !(thing instanceof Square);
var largerThan10 = isShape && thing.size > 10;
if (isShape && notSquare && largerThan10) {
console.log('some big polygon');
}
```
*Wrong:*
```js
if (
thing instanceof Shape
&& !(thing instanceof Square)
&& thing.size > 10
) {
console.log('bigger than ten?? Woah!');
}
```
## Name regular expressions
*Right:*
```js
var validPasswordRE = /^(?=.*\d).{4,}$/;
if (password.length >= 4 && validPasswordRE.test(password)) {
console.log('password is valid');
}
```
*Wrong:*
```js
if (password.length >= 4 && /^(?=.*\d).{4,}$/.test(password)) {
console.log('losing');
}
```
## Write small functions
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.
## Return early from functions
To avoid deep nesting of if-statements, always return a function's value as early
as possible.
*Right:*
```js
function isPercentage(val) {
if (val <0)returnfalse;
if (val > 100) return false;
return true;
}
```
*Wrong:*
```js
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:
```js
function isPercentage(val) {
var isInRange = (val >= 0 && val <= 100);
return isInRange;
}
```
## Name your closures
Feel free to give your closures a descriptive name. It shows that you care about them, and
will produce better stack traces, heap and cpu profiles.
*Right:*
```js
req.on('end', function onEnd() {
console.log('winning');
});
```
*Wrong:*
```js
req.on('end', function() {
console.log('losing');
});
```
## No nested closures
Use closures, but don't nest them. Otherwise your code will become a mess.
*Right:*
```js
setTimeout(function() {
client.connect(afterConnect);
}, 1000);
function afterConnect() {
console.log('winning');
}
```
*Wrong:*
```js
setTimeout(function() {
client.connect(function() {
console.log('losing');
});
}, 1000);
```
## Use slashes for comments
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**.
***Exception:*** Comment blocks describing a function and it's arguments (docblock) should start with `/**`, contain a single `*` at the begining of each line, and end with `*/`.
var matches = item.match(/ID_([^\n]+)=([^\n]+)/));
/**
* Fetches a user from...
*@param {string} id - id of the user
*@return {Promise}
*/
function loadUser(id) {
// 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.
...
}
var isSessionValid = (session.expires <Date.now());
if (isSessionValid) {
...
}
```
*Wrong:*
```js
// 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) {
// ...
}
```
## Classes/Constructors and Inheritance
While JavaScript it is not always considered an object-oriented language, it does have the building blocks for writing object oriented code. Of course, as with all things JavaScript, there are many ways this can be accomplished. Generally, we try to err on the side of readability.
### Capitalized function definition as Constructors
When Defining a Class/Constructor, use the function definition syntax.
*Right:*
```js
function ClassName() {
}
```
*Wrong:*
```js
var ClassName = function () {};
```
### Inhertiance should be done with a utility
While you can do it with pure JS, a utility will remove a lot of boilerplate, and be more readable and functional.
*Right:*
```js
// uses a lodash inherits mixin
// inheritance is defined first - it's easier to read and the function will be hoisted
_(Square).inherits(Shape);
function Square(width, height) {
Square.Super.call(this);
}
```
*Wrong:*
```js
function Square(width, height) {
this.width = width;
this.height = height;
}
Square.prototype = Object.create(Shape);
```
### Keep Constructors Small
It is often the case that there are properties that can't be defined on the prototype, or work that needs to be done to completely create an object (like call it's Super class). This is all that should be done within constructors.
Try to follow the [Write small functions](#write-small-functions) rule here too.
### Use the prototype
If a method/property *can* go on the prototype, it probably should.
```js
function Square() {
...
}
/**
* method does stuff
*@return {undefined}
*/
Square.prototype.method = function () {
...
}
```
### Handling scope and aliasing `this`
When creating a prototyped class, each method should almost always start with:
`var self = this;`
With the exception of very short methods (roughly 3 lines or less), `self` should always be used in place of `this`.
var ExternalClass = Private(require('path/to/some/class'));
...
});
```
### Promises
A more robust version of Angular's `$q` service is available as `Promise`. It can be used in the same way as `$q`, but it comes packaged with several utility methods that provide many of the same useful utilities as Bluebird.
This Javascript guide forked from the [node style guide](https://github.com/felixge/node-style-guide) created by [Felix Geisendörfer](http://felixge.de/) and is
licensed under the [CC BY-SA 3.0](http://creativecommons.org/licenses/by-sa/3.0/)