Ternary operators with boolean literal - ew. How about "isDecl && (parent.type == ...".

Or, what about filtering on functions in the first place instead of having to look "up" to see if the parent is the right thign:

if (node.type == 'FunctionExpression' || node.type == 'FunctionDeclaration') {
  var block = node.body;
  ...
}