Task

Implement an iterator which receives an array of values, and returns an object with:

• a function next
• a number index

A call to the next function should return an object with 2 attributes:

• value (the next value in the input array; undefined if the value is not present or the array has been fully processed)
• done (boolean which specifies whether the input array has been fully processed)

Accessing the index attribute should return the index of the value currently held by the iterator.

Example:

const iterator = createIterator(['One', , 'Two']);

iterator.index  // 0
iterator.next() // { value: 'One', done: false }
iterator.index  // 1
  
// A hole in the array - value is undefined
iterator.next() // { value: undefined, done: false }
iterator.index  // 2

iterator.next() // { value: 'Two', done: false }
iterator.index  // 3

// Iteration has finished - value is undefined, done becomes true
iterator.next() // { value: undefined, done: true }
iterator.index  // 3

// Subsequent calls to next of a fully processed iterator don't change anything
iterator.next() // { value: undefined, done: true }
iterator.index  // 3