## Block Chain
### Instructions
Create a function named `blockChain` that creates a block in your very own block chain. It 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 `hashCode` function provided. You will need to pass it a concatenation of the block's `index` , the previous block's `hash` and the block's stringified `data` .
- `data` : any valid object.
- `prev` : the previous block.
- `chain` : a function that accepts `data` as an argument, and creates 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
- [JSON.stringify ](https://devdocs.io/javascript/global_objects/json/stringify )
### Code provided
> The provided code will be added to your solution, and does not need to be submitted.
```js
const hashCode = str =>
(
[...str].reduce((h, c) => (h = (h < < 5 ) - h + c . charCodeAt ( 0 ) ) & h , 0 ) > >> 0
).toString(36)
```
