Code an ERC 20 Token on Ethereum/Polygon or Matic chain

How to create your own crypto coin, ERC 20 token, based on ETH/Polygon or Matic chain.

Here is the simple code of standard ERC 20 token, follow the Token Standard (technical spec) EIP-20.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract DadJokes {

mapping (address => uint256) public balanceOf;
string public name = "DadJokes";
string public symbol = "DAJO";
uint8 public decimals = 18;
uint256 public totalSupply = 100000 * (10 ** decimals);
mapping (address => mapping (address => uint256)) public allowance;

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


constructor () { 
    balanceOf[msg.sender] = totalSupply;
    }

function transfer(address _to, uint256 _value) public returns (bool success) { 
    require(balanceOf[msg.sender] >= _value, "Not enough tokens to transfer."); 
    balanceOf[msg.sender] -= _value; 
    balanceOf[_to] += _value;
    emit Transfer(msg.sender, _to, _value); 
    return true; 

}

function transferfrom(address _from, address _to, uint256 _value) public returns (bool success) {
require(allowance[_from][msg.sender] >= _value, “Not approved to transfer.”);
require(balanceOf[_from] >= _value, “Not enough tokens to transfer.”);
balanceOf[_from] -= _value;
balanceOf[_to] += _value;
allowance[_from][msg.sender]-= _value;
emit Transfer(_from, _to, _value);
return true;
}
function approve(address _spender, uint256 _value) public returns (bool success) {
allowance[msg.sender][_spender] = _value;
emit Approval(msg.sender, _spender, _value);
return true;
}
}

I named this funny token DADJOKES and ticker is DAJO