Meteor : How to use ReactiveVar ?

Some times do you wan’t change values automatically in your page. In this situations you can use “ReactiveVar”.

ReactiveVar package : https://atmospherejs.com/meteor/reactive-var 

Oficial documentation : http://docs.meteor.com/#/full/reactivevar_pkg

Add the package : meteor add reactive-var

Example : I wan’t show a new letter when somebody click in a button .

For I have all letters, I will insert this when I startup my application.

config.js

Meteor.startup(function () {
    loadLetters();
});

function loadLetters(){

    if ( Letters.find({}).count() == 0 ){
        insertLettersDB();
    } else if ( Letters.find({}).count() != 25 ){
        removeLettersAll();
        insertLettersDB();
    }
}

function removeLettersAll(){
    Letters.find({}).forEach(
        function(i) {
            Letters.remove(i);
        }
    )
}

function insertLettersDB(){
    var count = 1;
    takeAllLetters().forEach(
        function(i) {
            Letters.insert({key:count,value:i})
            count += 1;
        }
    )
}

function takeAllLetters(){
    var letters = [
        'A','B','C','D','E',
        'F','G','H','I','J',
        'L','M','N','O','P',
        'Q','R','S','T','U',
        'V','X','Z','Y','K'
    ];
    return letters;
}

My collection :

letters-collections.js

Letters = new Mongo.Collection("letters");

My Html file :

home.html

{...}

{{#if isShowResult}}
    {{_ "stop-letter-is"}} {{letter}}
{{/if}} 

{...}

home.js

var letter = new ReactiveVar("");
Template.home.events({
    'click #start': function (e) {
        var id = getRandoInt(1,25);
        letter.set(Letters.findOne({key:id}).value);
    }
});


Template.home.helpers({
    'letter':function(){
        return letter.get();
    },
    isShowResult:function(){
        return letter.get().length > 0;
    }
});


function getRandoInt(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

Finally you can check how it works in : http://playstop.meteor.com/

If you want take all source of this example :  https://bitbucket.org/exemples/playstop