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CoffeeScript style guide

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ferencmurcsik edited this page Dec 19, 2014 · 3 revisions

CoffeeScript Style Guide for Pasha

This guideline presents our code-styling conventions for Pasha.

Inspiration

This document was heavily inspired by Polarmobile's Style Guide. We added/changed a few points in it.

Table of Contents

## Code layout ### Tabs or Spaces?

Use spaces only, with 4 spaces per indentation level. Never mix tabs and spaces.

### Maximum Line Length

Limit all lines to a maximum of 79 characters.

### Blank Lines

Separate top-level function and class definitions with a single blank line.

Separate method definitions inside of a class with a single blank line.

Use a single blank line within the bodies of methods or functions in cases where this improves readability (e.g., for the purpose of delineating logical sections).

### Trailing Whitespace

Do not include trailing whitespace on any lines.

### Commas in Arrays and Objects

Always separate Array items with a comma, even if they are on separate lines.
Avoid the use of commas between Object properties if they are on separate lines.

# Yes

foo = [
  'some',
  'string',
  'values'
]
bar:
  label: 'test'
  value: 87

# No
foo = [
  'some'
  'string'
  'values'
]
bar:
  label: 'test',
  value: 87
### Encoding

UTF-8 is the preferred source file encoding.

## Module Imports

If using a module system (CommonJS Modules, AMD, etc.), require statements should be placed on separate lines.

require 'lib/setup'
Backbone = require 'backbone'

These statements should be grouped in the following order:

  1. Standard library imports (if a standard library exists)
  2. Third party library imports
  3. Local imports (imports specific to this application or library) 
# Node imports (standard library)
path = require('path')
underscore = require('underscore')
nock = require('nock')
# Hubot imports (3rd party)
Robot = require('hubot/src/robot')
Message = require('hubot/src/message')
TextMessage = Message.TextMessage
# Pasha imports (app-specific)
Prio1 = require('../pasha_modules/model').Prio1
State = require('../pasha_modules/model').State
constant = require('../pasha_modules/constant').constant
pasha_main = require("../scripts/pasha_main")
## Whitespace in Expressions and Statements

Avoid extraneous whitespace in the following situations:

  • Immediately inside parentheses, brackets or braces

       ($ 'body') # Yes
   ( $ 'body' ) # No

  • Immediately before a comma

       console.log x, y # Yes
   console.log x , y # No

Additional recommendations:

  • Always surround these binary operators with a single space on either side

    • assignment: =

      • Note that this also applies when indicating default parameter value(s) in a function declaration

        test: (param = null) -> # Yes
test: (param=null) -> # No

    • augmented assignment: +=, -=, etc.

    • comparisons: ==, <, >, <=, >=, unless, etc.

    • arithmetic operators: +, -, *, /, etc.

    • (Do not use more than one space around these operators)

         # Yes
   x = 1
   y = 1
   fooBar = 3

   # No
   x      = 1
   y      = 1
   fooBar = 3
## Comments

If modifying code that is described by an existing comment, update the comment such that it accurately reflects the new code. (Ideally, improve the code to obviate the need for the comment, and delete the comment entirely.)

The first word of the comment should be capitalized, unless the first word is an identifier that begins with a lower-case letter.

If a comment is short, the period at the end can be omitted.

### Block Comments

Block comments apply to the block of code that follows them.

Each line of a block comment starts with a # and a single space, and should be indented at the same level of the code that it describes.

Paragraphs inside of block comments are separated by a line containing a single #.

  # This is a block comment. Note that if this were a real block
  # comment, we would actually be describing the proceeding code.
  #
  # This is the second paragraph of the same block comment. Note
  # that this paragraph was separated from the previous paragraph
  # by a line containing a single comment character.

  init()
  start()
  stop()
### Inline Comments

Inline comments are placed on the line immediately above the statement that they are describing. If the inline comment is sufficiently short, it can be placed on the same line as the statement (separated by a single space from the end of the statement).

All inline comments should start with a # and a single space.

The use of inline comments should be limited, because their existence is typically a sign of a code smell.

Do not use inline comments when they state the obvious:

  # No
  x = x + 1 # Increment x

However, inline comments can be useful in certain scenarios:

  # Yes
  x = x + 1 # Compensate for border
## Naming Conventions

Use camelCase (with a leading lowercase character) to name all variables, methods, and object properties.

Use CamelCase (with a leading uppercase character) to name all classes. (This style is also commonly referred to as PascalCase, CamelCaps, or CapWords, among other alternatives.)

(The official CoffeeScript convention is camelcase, because this simplifies interoperability with JavaScript. For more on this decision, see here.)

For constants, use all uppercase with underscores:

CONSTANT_LIKE_THIS

Methods and variables that are intended to be "private" should begin with a leading underscore:

_privateMethod: ->
## Functions

(These guidelines also apply to the methods of a class.)

When declaring a function that takes arguments, always use a single space after the closing parenthesis of the arguments list:

foo = (arg1, arg2) -> # Yes
foo = (arg1, arg2)-> # No

Always use parentheses when declaring functions, even if they take no arguments:

bar = () -> # Yes
bar = -> # No

In cases where method calls are being chained and the code does not fit on a single line, each call should be placed on a separate line and indented by one level (i.e., four spaces), with a leading ..

[1..3]
  .map((x) -> x * x)
  .concat([10..12])
  .filter((x) -> x < 11)
  .reduce((x, y) -> x + y)

When calling functions, choose to omit or include parentheses in such a way that optimizes for readability. Keeping in mind that "readability" can be subjective, the following examples demonstrate cases where parentheses have been omitted or included in a manner that the community deems to be optimal:

baz 12

brush.ellipse x: 10, y: 20 # Braces can also be omitted or included for readability

foo(4).bar(8)

obj.value(10, 20) / obj.value(20, 10)

print inspect value

new Tag(new Value(a, b), new Arg(c))

Do not use parentheses to group functions like this:

($ '#selektor').addClass 'klass' # -> No

(foo 4).bar 8 # -> No

Use the following syntax instead:

$('#selektor').addClass 'klass' # -> Yes

foo(4).bar 8 # -> Yes
## Strings

Use string interpolation instead of string concatenation:

"this is an #{adjective} string" # Yes
"this is an " + adjective + " string" # No

Prefer single quoted strings ('') instead of double quoted ("") strings, unless features like string interpolation are being used for the given string.

## Conditionals

Favor unless over if for negative conditions.

Instead of using unless...else, use if...else:

  # Yes
  if true
    ...
  else
    ...

  # No
  unless false
    ...
  else
    ...

Multi-line if/else clauses should use indentation:

  # Yes
  if true
    ...
  else
    ...

  # No
  if true then ...
  else ...
## Looping and Comprehensions

Take advantage of comprehensions whenever possible:

  # Yes
  result = (item.name for item in array)

  # No
  results = []
  for item in array
    results.push item.name

To filter:

result = (item for item in array when item.name is "test")

To iterate over the keys and values of objects:

object = one: 1, two: 2
alert("#{key} = #{value}") for key, value of object
## Extending Native Objects

Do not modify native objects.

For example, do not modify Array.prototype to introduce Array#forEach.

## Exceptions

Do not suppress exceptions.

## Annotations

Let's keep annotations simple: only use TODO, to mark something needs to be done there.
This is our preference, over using various categories (TODO, FIXME, OPTIMIZE, HACK, REVIEW)

Write the annotation on the line immediately above the code that the annotation is describing.
The annotation keyword should be followed by a colon and a space, and a descriptive note.

  # TODO: The client's current state should *not* affect payload processing.
  resetClientState()
  processPayload()

If multiple lines are required by the description, indent subsequent lines with 4 spaces:

  # TODO: Ensure that the value returned by this call falls within a certain
  #   range, or throw an exception.
  analyze()
## Miscellaneous

and is preferred over &&.

or is preferred over ||.

is is preferred over ==.

not is preferred over !.

or= should be avoided:

temp = temp || {} # Yes
temp or= {} # No

Prefer shorthand notation (::) for accessing an object's prototype:

Array::slice # Yes
Array.prototype.slice # No

Prefer @property over this.property.

return @property # Yes
return this.property # No

However, avoid the use of standalone @:

return this # Yes
return @ # No

Avoid return where not required, unless the explicit return increases clarity.

Use splats (...) when working with functions that accept variable numbers of arguments:

console.log args... # Yes

(a, b, c, rest...) -> # Yes

##Useful resources

Pasha

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