CoffeeScript command mode

Command mode

Problem

You need to have another object handle your own executable code.

Solution

Use Command pattern to pass a reference to a function.

# Using a private variable to simulate external scripts or modules
incrementers = (() ->
    privateVar = 0

    singleIncrementer = () ->
        privateVar += 1

    doubleIncrementer = () ->
        privateVar += 2

    commands = 
        single: singleIncrementer
        double: doubleIncrementer
        value: -> privateVar
)()

class RunsAll
    constructor: (@commands...) ->
    run: -> command() for command in @commands

runner = new RunsAll(incrementers.single, incrementers.double, incrementers.single, incrementers.double)
runner.run()
incrementers.value() # => 6

Discuss

With the function as a first-level object and inherited from the variable range of the Javascript function, CoffeeScript makes the language pattern almost visible. In fact, any function that passes a callback function can act as a command.

The jqXHR object returns the jQuery AJAX method using this pattern.

jqxhr = $.ajax
    url: "/"

logMessages = ""

jqxhr.success -> logMessages += "Success!\n"
jqxhr.error -> logMessages += "Error!\n"
jqxhr.complete -> logMessages += "Completed!\n"

# On a valid AJAX request:
# logMessages == "Success!\nCompleted!\n"