latest change CP

controllers.application.js

import Ember from 'ember';

function latestProperty(dependentKeyA, dependentKeyB, latestWin = false) {
  let aTimestamp, bTimestamp;
  aTimestamp = bTimestamp = + new Date();
  let aCache, bCache;
  return Ember.computed(dependentKeyA, dependentKeyB, function() {
    let currentA = Ember.get(this, dependentKeyA);
    let currentB = Ember.get(this, dependentKeyB);
    let timestamp = + new Date();
    
    if (currentA !== aCache) {
      aCache = currentA;
      aTimestamp = timestamp;
    }
    if (currentB !== bCache) {
      bCache = currentB;
      bTimestamp = timestamp;
    }
    
    if (aTimestamp === bTimestamp) {
      return latestWin ? dependentKeyA : dependentKeyB;
    } else if (aTimestamp > bTimestamp) {
      return dependentKeyA;
    } else {
      return dependentKeyB;
    }
  });
}

function latestValue(dependentKeyA, dependentKeyB, latestWin = false) {
  let aTimestamp, bTimestamp;
  aTimestamp = bTimestamp = + new Date();
  let aCache, bCache;
  return Ember.computed(dependentKeyA, dependentKeyB, function() {
    let currentA = Ember.get(this, dependentKeyA);
    let currentB = Ember.get(this, dependentKeyB);
    let timestamp = + new Date();
    
    if (currentA !== aCache) {
      aCache = currentA;
      aTimestamp = timestamp;
    }
    if (currentB !== bCache) {
      bCache = currentB;
      bTimestamp = timestamp;
    }
    
    if (aTimestamp === bTimestamp) {
      return latestWin ? currentA : currentB;
    } else if (aTimestamp > bTimestamp) {
      return currentA;
    } else {
      return currentB;
    }
  });
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  valueA: 'aaaa',
  valueB: 'bbbb',
  
  latestChangeValue: latestValue('valueA', 'valueB'),
  
  latestChangeProperty: latestProperty('valueA', 'valueB')
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
Value A: {{input value=valueA}}
<br>
<br>
Value B: {{input value=valueB}}
<br>
<br>
Latest value comes from: {{latestChangeProperty}}
<br>
and is equal to: {{latestChangeValue}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}