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## Block Chain
### Instructions
Create a `blockChain` that create a block in your very own block chain.
the function takes 2 arguments:
- `data` any valid JSON data
- `prev` the previous block, if no block are given it should use the
genesis block: `{ index: 0, hash: '0' }`
A block must have the following properties:
- `index`
- `hash` a computed hash using the concatenation of the `index`, `hash`
and stringified `data` and hashing all of it using the provided `hashCode`.
- `data` the data (not encoded in JSON)
- `prev` the previous block
- `chain` a function that takes a new `data` and create the next block with it.
### Examples
```js
const first = blockChain({ a: 1 })
console.log(first.index) // -> 1
console.log(first.data) // -> { a: 1 }
console.log(first.prev) // -> { index: 0, hash: "0" }
console.log(first.hash) // -> '1103f27'
console.log(hashCode('10{"a":1}')) // -> '1103f27'
const second = first.chain({ hello: 'world' })
console.log(second.hash) // -> '18drvvc'
console.log(hashCode('21103f27{"hello":"world"}')) // -> '18drvvc'
const chain = second
.chain({ value: 4455 })
.chain({ some: 'data' })
.chain({ cool: 'stuff' })
const fork = second
.chain({ value: 335 })
.chain({ some: 'data' })
.chain({ cool: 'stuff' })
console.log(chain.hash) // -> '1qr3qfs'
console.log(fork.hash) // -> '1x9gsc1'
console.log(chain.index) // -> 5
console.log(fork.index) // -> 5
```
### Notions
- [devdocs.io/javascript/global_objects/json/stringify](https://devdocs.io/javascript/global_objects/json/stringify)
### Code provided
```js
const hashCode = str =>
(
[...str].reduce((h, c) => (h = (h << 5) - h + c.charCodeAt(0)) & h, 0) >>> 0
).toString(36)
```