Why Is Redux State Immutable?

For Redux to work correctly, the state must be immutable. This means that whenever we update the Redux state, we have to create a copy of the whole state and set values to fields we want to change. In code, this usually looks like this:

let newState = {
    ...oldState,
    field1: {
        ...oldState.field1,
        field2: "someNewValue"
    },
}