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I am building a framework for ERC20 tokens.

Aim is to scan all events (Transfer and Approve) generated by ERC20 contract, for which I am using web3.js getPastEvents.

I have set the toBlock to web3.eth.getBlockNumber() i.e. latest block

Now, to avoid scanning unnecessary blocks, I have to set fromBlock option. Can someone explain how to get block's number of the block in which erc20 token was deployed?

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There is no fast/elegant way to get the first transaction to an ethereum address/contract.

I will avoid scanning each block from the beginning.

What I will do is start from the top of the chain ( latest block) 10,000 blocks at a time and read all the events.

Once I get 0 events in the last 10,000 blocks I will stop.

That seems to be a working (not very elegant) solution.

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    Alternatively you can do a binary search on web3.eth.getCode to find the block it was created in.
    – natewelch_
    Jul 13 '18 at 21:35
  • Kindly elaborate, getcode return the compiled code of contract. How to parse the block number from it?
    – Karan
    Jul 14 '18 at 11:39
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    You can supply a block number to gerCode, so you can do a binary search on the results of that. If it returns bytecode, it's already been created. If it doesn't return bytecode then it hasn't been created yet.
    – natewelch_
    Jul 14 '18 at 12:05
  • Got it. in my method, I am storing the parsed events. If i run sequential/parallel queries for get code till the block where getCode returns nothing, net number of queries will be 2X (getCode + getAllEvents). your solution is better in terms of network data being returned, but for my use case it will make the script heavier..
    – Karan
    Jul 14 '18 at 13:03
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If you are in the control of the smart contract, emit a 'Deployed' event in the constructor. Then scan for these events.

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