Have you checked Atmosphere for packages to help you accomplish this?.. I have a whole array of packages written under the Socialize namespace that help to implement social features into meteor apps. Specifically the Likeable packages helps to create models that can be liked and seems to be exactly what you are looking for.
you can create a Combination mongo database which can store a key combination.
Say
MeteoruserId()+’ '+this.Id
Once a user clicks on like button the first time the key gets stored in the combination databse and the number of likes increase by 1.
But when the user tries to click the like button again you can check for the combination in the database.The code can be–
AnswerLikes=new Mongo.Collection(‘answerlikes’);
‘click button’:function(event){
event.preventDefault();
var documentId = this._id;
var currentUser=Meteor.userId();
var clickCombination=documentId+’ '+Meteor.userId();
if (AnswerLikes.findOne({combination:clickCombination})== undefined)
{