Sebastien Rousseau


The making of the Express Transaction Credits Platform - EXTC

by (7 minute read)

Tags: blockchain credits cryptocurrencies distributed eip erc20 erc223 ethereum extc extc-network extc-token faster financial ganache metamask payment ropsten services smart-contracts solidity standard test token tokens transaction transfer truffle

Building a comprehensive framework of the next generation of ERC-223 compliant tokens

The ERC-223 Token Standard Banner


In this article, we’ll be looking at building our decentralised exchange structured around the ERC223 standard - a superset of the ERC20 token standard compliant with the proposed ERC223 EIP standard interfaces for Tokens and APIs within smart contracts and part of the Ethereum blockchain technology stack.


The name we have chosen for our token is EXTC (Express Transaction Credits) with a vision to achieve a brand new suite of financial services facilitating and guaranteeing instant loans, lighting-fast payments and swifter deposits between participants.

Let’s get started on the premise that:

  • EXTC is an Ethereum based ERC223 and ERC223 EIP compliant token/smart-contract

  • The Express Transaction Credits services will support traditional fiat currencies, cryptocurrencies and compliant tokens through a set of smart contracts

  • The smart contracts are written in Solidity

  • We will use Truffle - a framework for creating smart contracts and decentralised applications - to test and deploy

  • We will use Ganache as the development environment, testing framework and asset pipeline, part of the Truffle suite of Ethereum development tools.

  • Metamask to make transactions on Ethereum through Chrome on the Ropsten Testnet Ethereum BlockChain Explorer and Search


  • NodeJS 6.11.5+ recommended
  • Yarn 1.3.2+ recommended
  • Mac OS X, Linux or Windows


# Install the Truffle package globally
$ npm install -g truffle
# Install local node dependencies, using the npm command:
$ npm install


# Install local node dependencies, using the yarn command:
$ yarn

Initialising the Token

The first step is to create a token contract file.

touch contracts/ExtcToken.sol

Defining the Token parameters

To create an ERC223 contract, you will also need to define the following values:

  • The Token’s Name
  • The Token’s Symbol
  • The Token’s Decimal Places
  • The Number of Tokens in Circulation

This will result to a similar declaration:

	string public name    = “Token”;
 	string public symbol  = “EXTC”;
 	uint8 public decimals = 18;
 	uint256 public totalSupply;

The following describes the standard functions and methods of the Express Transaction Credits contract.

  • name of the token (e.g Express Transaction Credits) -typically a string
  // Function to access name of token .
  function name() constant returns (string _name) {
      return name;
  • symbol of the token (EXTC) - represented as an uint8
  // Function to access symbol of token .
  function symbol() constant returns (string _symbol) {
      return symbol;
  • decimals the decimal values of the token - a unassigned Integer representing the number of digits that come after the decimal place. (e.g 18)
// Function to access decimals of token .
  function decimals() constant returns (uint8 _decimals) {
      return decimals;
  • totalSupply of the token equals the sum of all balances
  // Function to access total supply of tokens .
  function totalSupply() constant returns (uint256 _totalSupply) {
      return totalSupply;
  • balanceOf Returns the account balance of another account with address _owner
function balanceOf(address _owner) constant returns (uint256 balance)
  • transfer(address, uint) Transfer the specified amount of tokens to the specified address. Needed due to backwards compatibility reasons with ERC20.
function transfer(address _to, uint _value) returns (bool)
  • transfer(address, uint, bytes) Transfer the specified amount of tokens to the specified address.
function transfer(address _to, uint _value, bytes _data) returns (bool)

Standard ERC-223 token functions

EXTC tokens by design are moving towards the Ethereum’s Improvement Proposal 223 (ERC223 EIP) Standard for ERC223 token and the standard API for tokens within smart contracts.

  • contract ExtcToken is ERC223Interface - Reference implementation of the ERC223 EXTC token

  • function ExtcToken - Assigns the totalSupply to the contract.

  • function balanceOf(address _owner) Gets the balance of the specified address. Returns an uint256 representing the amount owned by the passed address.

  • function allowance(address _owner, address _spender) - displays the amount of remaining tokens allowed to spent