How Do I Create Meteor Template Helper to Check Equality?

Question

I am making a chat web app. people can login with facebook and talk (insert message into mongoDB).

showing the text is simple: javascript:

  messages: function () {
    return Messages.find({}, {sort: {createdAt: 1}});
  } 

each message has these attributes:

text: text,
      createdAt: new Date(),            // current time
      owner: Meteor.userId(),           // _id of logged in user
      username: Meteor.user().profile.name

It works fine, but I want to "style the message differently" depending on whether the message's owner is equal to currentUser (i.e. whether it's my message or others message)

For example, I want my message to be float:right and others message to be float:left

I am thinking the code probably looks something like this:

  {{#if mymsg}}
    <div class="msgdiv_my">
       <span class="message">{{text}}</span>
    </div>
  {{else}}
    <div class="msgdiv">
      <span class="message">{{text}}</span>
    </div>
  {{/if}}

Where and how to write the mymsg function (which should return True if the message.owner == currentUser, and false otherwise)

Answer 1

You would usually write those checks in a template helper, like this:

Template.myTemplate.helpers({
  ownDocument: function (doc) {
    return doc.owner === Meteor.userId();
  }
});

Then in myTemplate, call your helper like this:

<template name="myTemplate">
  {{#if ownDocument text}}
    <div class="msgdiv_my">
       <span class="message">{{text}}</span>
    </div>
  {{else}}
    <div class="msgdiv">
      <span class="message">{{text}}</span>
    </div>
  {{/if}}
</template>

Although you may want to implement a global "equals" helper to your meteor app's client, as it sadly is not built in Meteor Spacebars yet:

Template.registerHelper('equals',
    function(v1, v2) {
        return (v1 === v2);
    }
);

This way, you would call:

{{#if equals text.owner currentUser._id}}

And get the same result.

KyleMit wrote a lengthy answer for all your equality check needs in Meteor.