How to set value of dropdown field to variable

How to set value of dropdown field to variable

For the life of me, I can't figure out why the following code won't set input.status to the previousSelection. 

Steps to reproduce:
1. Click input.complete
2. input.status dropdown updates from '1-Backlog' to '4-Done'
3. Click input.complete again to deselect it
4. Expected: input.status updates to previousSelection (1-Backlog)
5. Actual: input.status displays empty

Code:
previousSelection = input.status;

// Check if the completed checkbox is checked
if(input.completed == true)
{
input.completed_date = now;
input.status = "4-Done";
}
else
{
// When not completed
input.completed_date = null;
input.sort_target_date = input.target_date;
//
// Revert to the stored previous status if there is one - Not working
input.status = previousSelection;

// Clear previousSelection to avoid looping
previousSelection = null;
}