Redux - How to add entry to array in reducer

If you're trying to add an element to the end of the entryName array you should be doing:

return {  ...state,  [entryId]: {    ...state[entryId],    [entryName]: [      ...state[entryId][entryName],      uniqueEntry    ]  }};

ES6 spread with arrays works like this:

const array1 = [1, 2, 3];const array2 = [4, 5, 6];const eight = 8;const newArray = ['stuff', ...array1, 'things', ...array2, ...[7, eight], 9];console.log(newArray); // ["stuff", 1, 2, 3, "things", 4, 5, 6, 7, 8, 9]

Check out this gist which has an example of something very similar to what you're doing.

I found this set of examples extremely helpful as well. A lot of great stuff in here:

https://github.com/sebmarkbage/ecmascript-rest-spread

Update:

If entryName is initialized to undefined like you say in your comment, you could do this:

return {  ...state,  [entryId]: {    ...state[entryId],    [entryName]: [      ...state[entryId][entryName] || [],      uniqueEntry    ]  }};

I think this is a pretty great example of how painful it can be working with React/redux using a heavily nested data structure. FWIW, it's been recommended to me many times to flatten your state as much as possible.