I want to check if a parent node equals a certain type as defined in the JSON data. Using d3.js v4 (yes I know...)

For example in the JSON:

{"name":"ABC", "type":"3program_outcome_group","children":[{"name":"XY","type":"program_outcome"},...

In this example, I want to check if parent node's type ('type' being a custom parameter) is equal to 3program_outcome_group. At the same time, I also need to check if the child node is of type program_outcome.

I have tried:

if (d.type == 'program_outcome' && d.parentNode.type == '3program_outcome_group' )
    return d.name.substring(0, 6);

But it's not working...

Whereas the following works without checking the parentNode:

if (d.type == 'program_outcome')
     return d.name.substring(0, 4);

I have also tried:

if (d.type == 'program_outcome' && this.parentNode.type == '3program_outcome_group' )
       return d.name.substring(0, 6);