MergedContacts | Contact Viewer app for the Locker Project

You can take advantage of checked: true on the data that is coming from the API. This data, you are already storing on the mergedContacts - so you can use it as a flag if this object is initially checked. This will be used later on, on assessing whether or not to push to contacts or deselectedContacts.

With that said, I took a look at your ToggleOption component, and it looks like you are already passing that object attribute as a prop named ischecked, and furthermore, you are not mutating it - which makes the job easier.

What I did is I passed additional props to the ToggleOption component, the deselectedContacts state and the setDeselectedContacts state setter. After that, on the onChange/onClick events of the ToggleOption inputs, I passed along the ischecked prop which would indicate if the contact was initially checked.