Chaining Promises in Coffeescript

Question

Is there a way to chain Promises together in Coffeescript. For example, consider the following javascript code,

return $.getJSON('/api/post.json')   .then(function(response) {     // do something   })   .then(function(response) {     // do something   })   .then(null, function(err) {     // do something   }); 

Each of the then's is optional, and the final then needs to be returned by the function. Currently I am writing this in coffeescript as,

promise = $.getJSON('/api/post.json') promise = promise.then (response) ->   // do something  promise = promise.then (response) ->   // do something  promise = promise.then null, (err) ->   // do something  return promise 

Is there a better way to do this? Thanks.

Answer 1

Ezekiel shows the right way, but it doesn't need the parentheses around the functions. Just do:

$.getJSON '/api/post.json' # As of CoffeeScript 1.7, you don't need the parentheses here either. .then (response) ->   # do something   response # if you would not return anything, promise would be fulfilled with undefined .then (response) ->   # do something   undefined # necessary to prevent empty function body .then null, (err) ->   # handle error 

I think it's surprisingly clean. The one thing that's relatively messy is when you need to add onRejected and onFulfilled handlers at the same time.

Note: Last time I checked, this did not work in CoffeeScript Redux, but this was a few months ago.

Note 2: You need at least one line of actual code (i.e. not just a comment) in each function body for this to work. Typically, you will, so it's not a big issue.