How to combine JSON objects with equal values within Backbone.js

Question

I am trying to display multiple "unread" alerts, but need to attach the organizations label to it if the organizations id is equal to the unread domainId.

How can I acheive this while displaying the results in a handlebars #each function?

JSON

"alerts" : {
    "organizations" : [ {
      "id" : 165,
      "label" : "Label #1"
    }, { 
      "id" : 170,
      "label" : "Label #2"
    }],
    "unread" : [ {
      "id" : 20022,
      "domainId" : 170,
      "created" : "2015-10-13T16:48:08Z",
    }, {    
      "id" : 20022,
      "domainId" : 165,
      "created" : "2015-10-13T16:48:08Z",
    }]
};

Backbone.js:

context: function() {
  var d = this.options.data 

  return {
    welcomeAlerts: d.alerts,
    welcomeOrg: d.alerts.organizations.label            
    }
},

Handlebars//HTMl

{{#each welcomeAlerts.unread}}
  <li class="alert-item stripe-list-item">
     <h4 class="org">{{welcomeOrg}}</h4>
     <h4 class="timestamp">{{created}}</h4>
  </li>  
{{/each}}

Answer 1

Simply transform the data beforehand

var data = {
 "alerts" : {
    "organizations" : [ {
      "id" : 165,
      "label" : "Label #1"
    }, { 
      "id" : 170,
      "label" : "Label #2"
    }],
    "unread" : [ {
      "id" : 20022,
      "domainId" : 170,
      "created" : "2015-10-13T16:48:08Z",
    }, {    
      "id" : 20022,
      "domainId" : 165,
      "created" : "2015-10-13T16:48:08Z",
    }]
 }
};

var organizationDict = _.groupBy(data.alerts.organizations, 'id');

var unreadWithOrganizations = _(data.alerts.unread)
  .map((message) => {
    return {
      ...message,
      organization: organizationDict[message.domainId]
    }
  })
  .value();

and display your data

{{#each unreadWithOrganizations}}
  <li class="alert-item stripe-list-item">
     <h4 class="org">{{organization.label}}</h4>
     <h4 class="timestamp">{{created}}</h4>
  </li>  
{{/each}}

Demo: http://jsbin.com/sadoluhepu/edit?js,console

I've made an example using lodash library and es6. You might want to stick with ES6 and underscore, which implementation might differ.