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Update blockchain readme example #836

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Aug 21, 2020
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Update blockchain readme example #836

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update readme example
ryanio Aug 18, 2020
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Merge branch 'master' into update-blockchain-readme
holgerd77 Aug 20, 2020
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Merge branch 'master' into update-blockchain-readme
holgerd77 Aug 21, 2020
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29 changes: 12 additions & 17 deletions packages/blockchain/README.md
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Expand Up @@ -24,29 +24,24 @@ The following is an example to iterate through an existing Geth DB (needs `level

This module performs write operations. Making a backup of your data before trying it is recommended. Otherwise, you can end up with a compromised DB state.

```javascript
const level = require('level')
const Blockchain = require('@ethereumjs/blockchain').default
const utils = require('ethereumjs-util')
```typescript
import Blockchain from '@ethereumjs/blockchain'
import { bufferToInt } from 'ethereumjs-util'
import level from 'level'

const gethDbPath = './chaindata' // Add your own path here. It will get modified, see remarks.

const db = level(gethDbPath)
const blockchain = new Blockchain({ db })

new Blockchain({ db: db }).iterator(
'i',
(block, reorg, cb) => {
const blockNumber = utils.bufferToInt(block.header.number)
const blockHash = block.hash().toString('hex')
console.log(`BLOCK ${blockNumber}: ${blockHash}`)
cb()
},
(err) => console.log(err || 'Done.'),
)
blockchain.iterator('i', (block) => {
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Is this intended to leave the await here?

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Yes the await would be useful for awaiting until the iterator is finished before moving onto the next line of code but since there is none I thought it’d be okay (and then I’d have to wrap it in an inner async func since you can’t await from the top level). I didn’t actually test it but I think it’ll work like that! Please correct me if I’m wrong :)

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I guess another option could be to add a .then(() => { console.log('Done.') }).catch(console.error)

const blockNumber = bufferToInt(block.header.number)
const blockHash = block.hash().toString('hex')
console.log(`Block ${blockNumber}: ${blockHash}`)
})
```

**WARNING**: Since `@ethereumjs/blockchain` is also doing write operations
on the DB for safety reasons only run this on a copy of your database, otherwise this might lead
to a compromised DB state.
**WARNING**: Since `@ethereumjs/blockchain` is also doing write operations on the DB for safety reasons only run this on a copy of your database, otherwise this might lead to a compromised DB state.

# EthereumJS

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