Cherry picking properties in CoffeeScript

Question

Is there a way in CoffeeScript to reduce the code size but still have the same effect as -

{hours, seconds, minutes} = data
x = {hours, seconds, minutes}

You can do it with [underscore pick method](http://underscorejs.org/#pick): `x = _.pick data, 'hours', 'seconds', 'minutes'`. — Leonid Beschastny, Nov 18 '13 at 16:56
@LeonidBeschastny using an external library is the only option? — tusharmath, Nov 18 '13 at 19:28
`x = { hours: data.hours, seconds: data.seconds, minutes: data.minutes }` — meager, Nov 18 '13 at 20:13

score 3 · Accepted Answer · answered Nov 19 '13 at 08:25

There are several ways to do it.

The best one is to adopt some helpful library, e.g. underscore or lodash:

x = _.pick data, 'hours', 'seconds', 'minutes'

But if you don't want to include external library to your project, then you may use one of the following methods.

Function call:

x = (->{@hours, @seconds, @minutes}).call data

Define custom reusable pick method:

Object::pick = (args...) ->
  res = {}
  res[k] = @[k] for k in [].concat args
  res

x = data.pick 'hours', 'seconds', 'minutes'

the second option look really neat. Thanks. – tusharmath Nov 19 '13 at 09:28 — tusharmath, Nov 19 '13 at 09:28

score 0 · Answer 2 · edited May 23 '17 at 12:31

In ES6, one idiom is

(({hours, seconds, minutes}) => ({hours, seconds, minutes})) (data)
  ^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^^^^^^^^^^^^^^^^^^^^^^^ 
  deconstruct argument           return object constructed 
  into variables                 using object literal
                                 shorthand
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^
                    DEFINE FAT ARROW FUNCTION                CALL IT

Whether you think is is good or horrible is ultimately a matter of personal preference.

What we really need is a pick operator in the language, so I could write

{hours, seconds, minutes} PICK data

For this I am proposing #, so

{hours, seconds, minutes} # data

Related: One-liner to take some properties from object in ES 6

Cherry picking properties in CoffeeScript

2 Answers2