ping-pong.js

/*

  In this challenge you will simulate the movement of a ping-pong, bouncing back and forth across a
  table.

  Create a function `pingPong` that accepts an array, and returns the *same* array
  with the ping-pong moved one cell. Each time the ping-pong moves, you must increment the
  ping-pong's `steps` counter by 1. The direction of movement should be determined soley by the
  current state of the array and the current `steps` value of the ping-pong.

  ``` javascript
  var table = [{steps: 0}, null, null, null];

  pingPong(table); //=> [null, {steps: 1}, null, null]
  pingPong(table); //=> [null, null, {steps: 2}, null]
  pingPong(table); //=> [null, null, null, {steps: 3}]
  pingPong(table); //=> [null, null, {steps: 4}, null]
  pingPong(table); //=> [null, {steps: 5}, null, null]
  pingPong(table); //=> [{steps: 6}, null, null, null]
  pingPong(table); //=> [null, {steps: 7}, null, null]

  table; //=> [null, {steps: 7}, null, null]
  ```

  Keep in mind that I should be able start this process at *any* point:

  ```
  var table = [null, {steps: 13}, null, null];
  pingPong(table); //=> [null, null, {steps: 14}, null]
  ```

  Bonuses
  - Allow arrays of *any length*
  - We can think of the ping-pong as having an internal "speed" of 1. Allow this value to be
    explicity set at a higher number (i.e. move 2 cells at a time, or 3 cells at a time).
  - Support multiple ping-pongs.

*/

// YOUR CODE HERE
function pingPong(arr){
  var stepcount = 0;
  for (i = 0; i < arr.length; i++){
    if (arr[i]){
      arr[i+1] = {steps: stepcount};
      stepcount ++;
    }
  }
}