I have an object as below:

```
var obj = 
{
  a : 
  {
    "x": "abc",
    "y": "def",
    "z": "ghi"
  },

 b : 
 {
   "p" : "jkl",
   "q" : "mno",
   "r" : "pqr"
 },
 ...
 ...
}

```

I want the output as below:

```
var targetObject = 
{
  "a_x":"abc",
  "a_y":"def",
  "a_z":"ghi",
..
..
..
..
}

```

There can be n number of key as well as hierarchy. Can we have a function where the input is the object and the output gives me that targetObject?