Extending a CoffeeScript class dynamically

Question

I know that a CoffeeScript class can be extended like this:

Dog::bark = ->
  console.log("bark")

I want to be able to do this dynamically. For example, I want to do something like this:

sounds = [ "bark", "woof", "grrr", "ruff" ] 

for sound in sounds
  Dog::[sound] = ->
    console.log(sound)

The equivalent JavaScript would be:

var sounds = [ "bark", "woof", "grrr", "ruff" ];

for (var i = 0; i < sounds.length; i++) 
{
  var sound = sounds[i];

  Dog.prototype[sound] = function() {
    console.log(sound);
  };
}

How can I do this with CoffeeScript?

mu is too short · Accepted Answer · 2013-04-06 22:52:42Z

4

You almost have it, you just need to toss a do in there to force sound to be evaluated when you build the new method:

sounds = [ "bark", "woof", "grrr", "ruff" ] 
for sound in sounds
    do (sound) ->
        Dog::[sound] = -> console.log(sound)

If you don't include the do you'll end up with all four methods doing console.log('ruff'). Adding the do converts the for loop's body to a self-executing function. From the fine manual (bottom of the section):

When using a JavaScript loop to generate functions, it's common to insert a closure wrapper in order to ensure that loop variables are closed over, and all the generated functions don't just share the final values. CoffeeScript provides the do keyword, which immediately invokes a passed function, forwarding any arguments.

Demo: http://jsfiddle.net/ambiguous/YAqJu/

answered Apr 6, 2013 at 22:52

mu is too short

436k71 gold badges863 silver badges822 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

LandonSchropp Over a year ago

Is Dog::[sound] really the correct syntax? I was just guessing.

mu is too short Over a year ago

@LandonSchropp: Yes it is. :: is just prototype and [sound] is a normal object property reference. So Dog::[sound] is the same as Dog.prototype[sound] and that's what you want to add methods.

LandonSchropp Over a year ago

Nice catch on the closure wrapper as well. I wasn't even thinking about that.

Collectives™ on Stack Overflow

Extending a CoffeeScript class dynamically

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related