I have an array of JSON object, for example, `people` with data, for example:

```
[
  {
    name : 'John',
    age : '7'
  },
  {
    name : 'Mary',
    age : '70'
  },
  {
    name : 'Joe',
    age : '40'
  },
  {
    name : 'Jenny',
    age : '4'
  }
]

```

I want to substitute all string values in `age` for its corresponding integer in order to sort by `age`. Or to add a key, for example `ageI` with the integer value. 

I could loop through the array, but, is there a better way to do that, for example with one command in jQuery?