Blockchain tokens existed before Ethereum.
- In some ways, the blockchain currency, Bitcoin, may be a token itself.
- There are many token platforms that were also developed on Bitcoin and other cryptocurrencies before Ethereum.
- The introduction of the first token standard on Ethereum led to an explosion of tokens.
Tokens standards (ERC20)
- The first standard was launched in November-2015 by Fabian Vogelsteller as an Ethereum Request for Comments (ERC). it had been automatically assigned Github issue number 20, giving rise to the name “ERC20 token”.
- The overwhelming majority of tokens are currently supported the ERC20 standard. ERC20 may be a standard for fungible tokens, meaning that different units of an ERC20 token are interchangeable and haven’t any unique properties.
- The ERC20 standard defines a standard interface for contracts implementing a token, such any compatible token is often accessed and utilized in an equivalent way.
ERC20 Required functions and events
total Supply:
Returns the entire units of this token that currently exist. ERC20 tokens can have a hard and fast or a variable supply.
balance Of:
Given an address, always returns the token balance of that address.
transfer:
Given an address and amount, transfers that quantity of tokens thereto address, from the balance of the address that executed the transfer.
transfer From:
Given a sender, recipient, and amount transfers tokens from one account to a different. utilized in combination with approval.
approve:
Given a recipient address and amount, authorizes that address to execute several transfers up thereto amount, from the account that issued the approval.
allowance:
Given an owner address and a spender address, must return the remaining amount that the spender is approved to withdraw from the owner.
Transfer:
The event depends upon a successful transfer(call to transfer or transfer From) even for zero-value transfers.
Approval:
Event logged upon a successful call to approve.