Retrieving data from a Meteor.call

The basics of Meteor.call

Meteor.call(name, [arg1, arg2...], [asyncCallback])

(1) name String
(2) Name of method to invoke
(3) arg1, arg2… EJSON-able Object [Optional]
(4) asyncCallback Function [Optional]

On one hand, you can do : (via Session variable, or via ReactiveVar)

    var syncCall = Meteor.call("mymethod") // Sync call

It mean if you do something like this, server side you will do :

    Meteor.methods({
        mymethod: function() {
            let asyncToSync =  Meteor.wrapAsync(asynchronousCall);
            // do something with the result;
            return  asyncToSync; 
        }
    });

On the other hand, sometimes you will want to keep it via the result of the callback ?

Client side :

Meteor.call("mymethod", argumentObjectorString, function (error, result) {
    if (error) Session.set("result", error); 
    else Session.set("result",result);
}
Session.get("result") -> will contain the result or the error;

//Session variable come with a tracker that trigger whenever a new value is set to the session variable. \ same behavior using ReactiveVar

Server side

Meteor.methods({
    mymethod: function(ObjectorString) {
        if (true) {
            return true;
        } else {
            throw new Meteor.Error("TitleOfError", "ReasonAndMessageOfError"); // This will and up in the error parameter of the Meteor.call
        }
    }
});

The purpose here is to show that Meteor propose various way to communicate between the Client and the Server.

Using Session variable

Server side

Meteor.methods({
  getData() {
    return 'Hello, world!';
  }
});

Client side

<template name="someData">
  {{#if someData}}
    <p>{{someData}}</p>
  {{else}}
    <p>Loading...</p>
  {{/if}}
</template>

Template.someData.onCreated(function() {
  Meteor.call('getData', function(err, res) {
    Session.set('someData', res);
  });
});

Template.someData.helpers({
  someData: function() {
    return Session.get('someData');
  }
});

Using ReactiveVar

Server side

Meteor.methods({
  getData() {
    return 'Hello, world!';
  }
});

Client side

<template name="someData">
  {{#if someData}}
    <p>{{someData}}</p>
  {{else}}
    <p>Loading...</p>
  {{/if}}
</template>

Template.someData.onCreated(function() {

  this.someData = new ReactiveVar();

  Meteor.call('getData', (err, res) => {
    this.someData.set(res);
  });
});

Template.someData.helpers({
  someData: function() {
    return Template.instance().someData.get();
  }
});

reactive-var package required. To add it run meteor add reactive-var.