DApp Development

Usage - Demo

You can easily create a sample working DApp with the following:

$ embark demo
$ cd embark_demo

To run the ethereum node for development purposes simply run:

$ embark blockchain

By default embark blockchain will mine a minimum amount of ether and will only mine when new transactions come in. This is quite usefull to keep a low CPU. The option can be configured at config/blockchain.yml

Then, in another command line:

$ embark run

This will automatically deploy the contracts, update their JS bindings and deploy your DApp to a local server at http://localhost:8000

Note that if you update your code it will automatically be re-deployed, contracts included. There is no need to restart embark, refreshing the page on the browser will do.

Creating a new DApp

$ embark new AppName
$ cd AppName

DApp Structure

  app/
    |___ contracts/ #solidity contracts
    |___ html/
    |___ css/
    |___ js/
  config/
    |___ blockchain.yml #environments configuration
    |___ contracts.yml  #contracts configuration
    |___ server.yml     #server configuration
  spec/
    |___ contracts/ #contracts tests

Solidity files in the contracts directory will automatically be deployed with embark run. Changes in any files will automatically be reflected in app, changes to contracts will result in a redeployment and update of their JS Bindings

Using Contracts

Embark will automatically take care of deployment for you and set all needed JS bindings. For example, the contract below:

# app/contracts/simple_storage.sol
contract SimpleStorage {
  uint storedData;
  function set(uint x) {
    storedData = x;
  }
  function get() constant returns (uint retVal) {
    return storedData;
  }
}

Will automatically be available in Javascript as:

# app/js/index.js
SimpleStorage.set(100);
SimpleStorage.get();

You can specify for each contract and environment its gas costs and arguments:

# config/contracts.yml
  development:
    SimpleStorage:
      gas_limit: 500000
      gas_price: 10000000000000
      args:
        - 100
  ...

If you are using multiple contracts, you can pass a reference to another contract as $ContractName, Embark will automatically replace this with the correct address for the contract.

# config/contracts.yml
  development:
    SimpleStorage:
      args:
        - 100
        - $MyStorage
    MyStorage:
       args:
         - "initial string"
    MyMainContract:
      args:
        - $SimpleStorage
  ...