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I'm having trouble properly understanding Meteor's reactivity and it's relation to contracts.

I've included the Ethereum Meteor packages ethereum:web3 and ethereum:blocks and read that EthBlocks.latest is reactive but my question is, how do I make a contract's function return reactive also? Am I suppose to hook into EthBlocks.latest somehow to run custom callbacks?

In the following DAPP I have a basic getter/setter contract (pingpong.sol), a Meteor template and associated template helpers and events.

Example:

pingpong.sol

contract pingpong {

    string public pong;
    // accessor function:
    // function pong() { return pong; }

    function ping (string val) {
        pong = val;
    }
}

main.html

<head>
  <title>pingpong</title>
</head>

<body>
  <h1>Ethereum DAPP Reactivity</h1>
  {{> pingpong}}
</body>

<Template name="pingpong">
  <h2>PONG - {{pong}}</h2>
  <form class="set-pong">
    <input type="text" name="text" placeholder="Type new pong value"/>
  </form>
</Template>

main.js

import { Template } from 'meteor/templating';
import { ReactiveVar } from 'meteor/reactive-var';

import './main.html';

// private chain
web3 = new Web3(new    Web3.providers.HttpProvider('http://localhost:8546'));

contract = web3.eth.contract([{"constant":false,"inputs":[{"name":"val","type":"string"}],"name":"ping","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"pong","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"}]);

ppInst = contract.at("0x8c3d23c31de790ac60a483ba47ea1b7fea08d67e");

EthBlocks.init();

Template.pingpong.onCreated(function pongCreated() {
    this.pong = new ReactiveVar(ppInst.pong());
})

Template.pingpong.helpers({
    pong() {
        return Template.instance().pong.get();
    }
})

Template.pingpong.events({
    'submit .set-pong'(event) {
        // Prevent default browser form submit
        event.preventDefault();

        ppInst.ping(event.target.text.value, {from:web3.eth.accounts[0]});

        //clear form
        event.target.text.value = '';
    },
})
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1 Answer 1

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Found Fabian's example of a simple meteor DAPP with excellent video tutorial and so included this in my code...

$ meteor add session

web3.eth.filter('latest').watch(function(e) {
    if(!e) {
        ppInst.pong(function(e, val) {
            Session.set('pong', val);
        });
    }
});

and changed my templates to:

Template.pingpong.onCreated(function pongCreated() {
        ppInst.pong(function(e, val) {
            Session.set('pong', val);
        });
})

Template.pingpong.helpers({
    pong() {
        return Session.get('pong');
    }
})
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