Question

I’m primarily a Rails developer, and so in whipping up a little script for my company’s Hubot instance, I was hoping to accomplish the following:

robot.brain.data.contacts ||= {}

Or, only make this new hash if it doesn’t already exist. The idea being that I want to have a contacts array added dynamically through the script so I don’t have to modify Hubot’s source, and I obviously don’t want to overwrite any contacts I add to it.

Question: is there a quick little construct like the Rails ||= that I can use in Coffeescript to achieve the above goal?

Cheers.

Answer 1

You can use ?= for conditional assignment:

speed ?= 75

The ? is the “Existential Operator” in CoffeeScript, so it will test for existence (not truthiness):

if (typeof speed === "undefined" || speed === null) speed = 75;

The resulting JS is a bit different in your case, though, because you are testing an object property, not just a variable, so robot.brain.data.contacts ?= {} results in the following:

var _base, _ref;
if ((_ref = (_base = robot.brain.data).contacts) != null) {
  _ref;
} else {
  _base.contacts = {};
};

More info: http://jashkenas.github.com/coffee-script/