(Reduce)Computed


functional big data transclusion in the browser

@jonnii




What is the best

feature of ember?




Routing?


Maybe...




Ember.Select?


Hahahahahaha. NO.




Computed Properties!!


Seriously, they are magic.




You know you can do this...





Did you know you can do this?


Computed Properties just reduced.

This is how I discovered reduce computed...




What is reduce computed?


A reduce computed is a computed property which
observes the state of an array and reduces it 
into a single value...

e.g.

Ember.computed.min
Ember.computed.max

It's the reduce part of map reduce. a.k.a Big Data.


Reduce Computed

  • initialValue
  • options
  • addedItem
  • removedItem

 Ember.computed.max = function (dependentKey) {
  return Ember.reduceComputed.call(null, dependentKey, {
    initialValue: -Infinity,

    addedItem: function (accumulatedValue, item, changeMeta, instanceMeta) {
      return Math.max(accumulatedValue, item);
    },

    removedItem: function (accumulatedValue, item, changeMeta, instanceMeta) {
      if (item < accumulatedValue) {
        return accumulatedValue;
      }
    }
  });
};

The secret sauce...


xxItem: function (accumulatedValue, item, changeMeta, instanceMeta) {
  ... magic ...    
},

changeMeta
index
item
arrayChanged
property


instanceMeta
A scratch pad for storing 
reduce computed state

Example Sum/Avg


Array Computed


Same as reduce computed except:

  • Result is an array
  • Result is kept up to date

For:

  • Filtering
  • Sorting

Group Example


What next?



Feature actively being worked on
Someone please rewrite Ember.Select

Plugs


Code Now
http://codenow.org/

I'm hiring... 

ReduceComputed

By Jonathan Goldman

ReduceComputed

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