Tokens on Ethereum

Blockchain tokens existed before Ethereum.

In some ways, the blockchain currency,Bitcoin, may be a token itself.
There are many any token platforms were also developed on Bitcoin and other cryptocurrencies before Ethereum.
Introduction of 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 standards for fungible tokens, meaning that different units of an ERC20 tokens are interchangeable and haven’t any unique properties.
The ERC20 standard defines a standard interface for contracts implementing a token, such any compatible token are 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 approve.

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 returns the remaining amount that the spender is approved to withdraw from the owner.

Transfer:
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.

Tokens on Ethereum