Clarification about reducers

I encountered the following code and I’m trying to make sense of it. When I substitute my simplified version of the code in question, the application doesn’t work.

The original code is:

const state = {count: 0}

const reducers = {
    add: (state) => ({count: state.count + 1}),
    sub: (state) => ({count: state.count - 1}),
}

My dumbed-down version is:

const myReducersAsAnObject = {
    add : function (state) {
        return count = state.count + 1
    },
    sub: function (state){
        return count = state.count - 1
    }
}

Where am I going wrong?