ERC-20

Introduction

This tutorial helps you to create an example ERC-20 compatible token that conforms to the Klaytn Token Standards, especially Fungible Token Standard (ERC-20).

ERC-20 Token Standard defines two events and 9 methods (including 3 optional methods) as below. ERC-20-compatible tokens are token contracts that implements the following interface.

function name() public view returns (string) //optional
function symbol() public view returns (string) //optional
function decimals() public view returns (uint8) //optional
function totalSupply() public view returns (uint256)
function balanceOf(address _owner) public view returns (uint256 balance)
function transfer(address _to, uint256 _value) public returns (bool success)
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
function approve(address _spender, uint256 _value) public returns (bool success)
function allowance(address _owner, address _spender) public view returns (uint256 remaining)

event Transfer(address indexed _from, address indexed _to, uint256 _value)
event Approval(address indexed _owner, address indexed _spender, uint256 _value)

Based on above interface, developers may customize tokens by adding new features and logics, and deploy on Klaytn network. For more information, refer to official ERC-20 documentation.

In this tutorial, you are going to implement MyERC20.sol, an ERC-20 compatible token. This token will issue a predefined amount of tokens and sends all of the tokens to the contract owner on its deploy.

MyERC20.sol is based on OpenZeppelin's ERC20 implementation. A major part of the code in this tutorial is forked from OpenZeppelin 2.3 and following Solidity files are used to implement MyERC20.sol.

• https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/IERC20.sol

• https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20.sol

• https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol

• https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/math/SafeMath.sol

The rest of this tutorial is organized as follows.

• 1. Writing ERC-20 smart contract

  • 1.1 Overall structure of MyERC20 code with whole MyERC20 code

  • 1.2 Take a look at important functions

• 2. Deploying smart contract

  • 2.1 Deploying smart contract using Klaytn IDE

  • 2.2 Deploying smart contract using truffle

• 3. Interacting between ERC-20 token and Klaytn wallet