PragPub 2011-08: Issue #26 by The Pragmatic Bookshelf

Author:The Pragmatic Bookshelf
Language: eng
Format: epub, mobi
Tags: PragPub—Monthly Magazine
Publisher: The Pragmatic Bookshelf, LLC
Published: 2011-08-01T04:00:00+00:00

Imagine No Dependencies

A lot of Node developers will tell you that attaching things to global rather than exports is a no-no. And if you’re packaging your code as a library, or trying to make your code reusable, then they’re right. But if you’re developing a standalone application, then go ahead and let yourself declare a few globals. In particular, if you’re using the pattern described in the last section, try adding this to your main application file:

global.world = world

Not only is this one line worth a thousand world = require 'world's, but it also makes the world dependency soft and easy to replace. At the top of your application’s tests, you could put this:

global.world = {

eventListeners: {}

emitCounts: {}

on: (event, func) -> (@eventListeners[event] ?= []).push func

emit: (event) -> @emitCounts[event] ?= 0; @emitCounts[event]++

}

Now none of the listeners attached to world will ever actually be fired, and you can easily run assertions on how many listeners are attached for a given event and how many times that event has occurred.

Alternatively, you can take the lighter tack of simply adding additional listeners for testing and selectively using EventEmitter::removeListener to halt those persistent monster screeches during unit testing. You might take advantage of the once method for your assertions, which acts just like on except one-time-only:

nasa = new EventEmitter

nasa.once 'land_on_moon', -> console.log 'Wow!'

nasa.emit 'land_on_moon' # Wow!

nasa.emit 'land_on_moon' # (silence)

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