State on the Chain

Tokens by hand: ERC-20 & ERC-721

Lesson 5 of 5

A token standard is just an interface everyone agreed on. Implement ERC-20 with allowances and see how ERC-721 changes one mapping to make every unit unique.

What you'll learn

Implement the ERC-20 core: transfer, approve, transferFrom and the allowance mapping
Explain the approve-then-pull pattern and why every DeFi app needs it
Contrast ERC-721's ownerOf(tokenId) with ERC-20's balanceOf and say what metadata is

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