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DAPP Using Meteor

This tutorial will show you how to setup a Meteor app to be used as a Ðapp and probably answer a few questions on why Meteor should used.

  1. Create your Ðapp
  2. Start your Ðapp
  3. Connect your Ðapp
  4. Run your Ðapp
  5. Add Ðapp styles
  6. Using ethereum:elements
  7. Ðapp code structure
  8. Bundle your Ðapp

FAQ

Isn't Meteor a full stack framework, how does that fit into Ðapp development

True, Meteor is a full stack framework and its main improvement is realtime web applications, but Meteor is also the first framework (i know of), which fully embraced single page app (SPA) development and provided all necessary tools.

5 reasons why Meteor is a perfect fit:

  1. Its purely written in JS and has all the tools a SPA needs (Templating engine, Model, on-the-fly compiling, bundling)
  2. You get a development environment, which has live reload, CSS injection and support for many pre-compilers (LESS, Coffeescript, etc) out of the box
  3. You can get all frontend code as single index.html with one js and css file plus your assets, using meteor-build-client. You can then host it everywhere or simple run the index.html itself or distribute it later on swarm.
  4. It embraces full reactivity, which make building consistent interface much easier (similar to angualr.js $scope or binding)
  5. It has a great model called Minimongo, which gives you a mongoDB like interface for a reactive in-memory database, which can also be auto-persistet to localstorage or indexedDB

Do i need to host my Ðapp on a server?

No, using meteor-build-client you can get all the static assets of you Ðapp to run without any server, though if you use a router like iron- or flow-router, you need to use hash (index.html#!/mypath) routes instead of clean HTML5 pushstate routes.

Create your Ðapp

Install Meteor if don't have already:

$ curl https://install.meteor.com/ | sh

Then create an app:

$ meteor create myDapp
$ cd myDapp

Next add the web3 package:

$ meteor add ethereum:web3

I recommend also to add the following packages:

  • ethereum:dapp-styles - The LESS/CSS framework which gives your dapp a nice Mist-consistent look.
  • ethereum:tools - This package gives you the EthTools object with a set of formatting an conversion functions and template helpers for ether.
  • ethereum:elements - A set of interface elements specifically made for ethereum, see this Demo for more.
  • ethereum:accounts - Gives you the reactive EthAccounts collection with all current available ethereum accounts, where balances will be automatically updated.
  • ethereum:blocks - Gives you the reactive EthBlocks collection with the latest 50 blocks. To get the lastest block use EthBlocks.latest (It will also have the latest default gasPrice)
  • frozeman:template-var - Gives you the TemplateVar object, that allows you to set reactive variables, which are template instance specific. See the readme for more.
  • frozeman:persistent-minimongo2 - Allows you to auto persist your minimongo collection in local storage

Start your Ðapp

A short excursion into Meteors folder structure

Meteor doesn't force you to have a specifc folder structure, though some folders have specifc meaning and will be treated differently when bundling/running your application.

Folders with specific treatment

  • client - files in a folder called client will only be loaded by the client part of your app and as we are building a Ðapp, thats where most of our files go.
  • lib - files in folders called lib will load before other files in the same folder. This is an ideal place your init files, libraries, or ethereum specifc files.
  • public - a folder called public contains assets meteor will make available on the root of your webserver (or later bundled Ðapp)
  • There are a few more specifc folders like server, tests, packages, etc. If you want to get to know them take a look at the Meteor docs

So to build a Ðapp we ideally create the following folder structure in our myDapp folder:

- myDapp
   - client
      - lib
      - myDapp.html
      - myDapp.js
      - myDapp.css
   - public

Note The community provides also Meteor Ðapp Boilerplates like this on from Nick Dodson: https://github.com/SilentCicero/meteor-dapp-boilerplate

Connect your Ðapp

To connect our dapp we need to start geth with the right CORS headers in another terminal:

$ geth --rpc --rpccorsdomain "http://localhost:3000"

We also need to set the provider. Ideally we create a file in our lib folder called init.js and add the following line:

// set providor
if(!web3.currentProvider) // make sure we don't overwrite a provider set by Mist later on
    web3.setProvider(new web3.providers.HttpProvider("http://localhost:8545"));

Run your Ðapp

Now we can run our Ðapp by simply running:

$ meteor

If we go to http://localhost:3000, we should see a website appear and if we open the browser console we can use the web3 object to query the geth node:

> web3.eth.accounts
['0xfff2b43a7433ddf50bb82227ed519cd6b142d382']

Add Ðapp styles

If you want your Ðapp to nicely fit later into Mist and have follow the official look use the dapp-styles css css/less framework.

Note that they are under heavy development and the class names and elements may change.

To add it simple add the following packages to your Ðapp:

$ meteor add less
$ meteor add ethereum:dapp-styles

Now rename you myDapp.css to myDapp.less and add the following line inside:

// libs
@import '{ethereum:dapp-styles}/dapp-styles.less';

Now you can use all dapp-styles classes and also overwrite all variables of the framework. You can find them in the repo. Overwrite them by copying them to your myDapp.less file and set different values.

Using ethereum packages

To make your live as a Ðapp developer easier we provide some packages that help you build Ðapps faster.

If you add the recommended packages above you should have the ethereum:tools, accounts and ethereum:blocks packages available.

These 3 packages give you the EthTools, EthAccounts and Ethblocks objects, which give you formatter functions, a collection with the accounts from web3.eth.accounts (with auto updated balance) and a collection of the last 50 blocks.

Most of these functions are reactive so they should make building interfaces a breeze.

Example usage

If you look into you myDapp.html you will find the hello template. Just add a helper called {{currentBlock}} some where between the <template name="hello">..</template> tags.

Now open the myDapp.js and add after the counter: function.. the currentBlock helper:

Template.elements.helpers({
    counter: function () {
      ...
    },
    currentBlock: function(){
        return EthBlocks.latest.number;
    }
  });

Then initialize EthBlocks by adding EthBlocks.init(); after Session.setDefault('counter', 0);

If you now check your Ðapp in the browser you should see the latest block number, which will increase once you mine.

For more examples please checkout the packages readmes and the demo (source) for more.

Ðapp code structure

This tutorial won't go into building apps with Meteor. For this please refer to the Meteor's tutorials, A list of good resources, EventMinded (payed tutorials) or books like Building Single-page Web Apps with Meteor or Discover Meteor.

TODO Short:

  • put ethereum related stuff into client/lib/ethereum/somefile.js
  • use myCollection.observe({added: func, changed: func, removed: func}) to communicate to ethereum, keep ethereum logic out of your app as much as possible. This way you just write and read from your reactive collections and the observe functions will handle the rest (e.g. sendTransactions)
  • Filters etc will add logs etc to your collections. So you keep all the callback mess out of your app logic.

For an example see the Ethereum-Wallet.

Bundle your Ðapp

To bundle your Ðapp into a local standalone file use meteor-build-client:

$ npm install -g meteor-build-client
$ cd myDapp
$ meteor-build-client ../build --path ""

This will put your Ðapps static files into the build folder, above your myDapp folder.

The last option --path will make the linking of all files relative, allowing you to start the app by simply clicking the build/index.html.

Be aware that when running your app on the file:// protocol, you won't be able to use client side routing, due to web security. Later in mist you will be able to use client side routing, as dapps are severed over the eth:// protocol.

In the future you will be able to simply upload your Ðapp on swarm.