How to modify array within object in react component state

Question

I have the following state in my app:

    const [activeChats, setActiveChats] = useState([
        {
          id: 1,
          name: 'Luciana Gutierrez',
          role: 'HR Manager',
          avatar: avatar2,
          messages: [
            {
              content: 'Hola Luciana! Tuviste alguna novedad?',
              received: false,
              date: '9:45 AM'
            },
            {
              content: 'Hola John! Todavía no...',
              received: true,
              date: '10:19 AM'
            },
            {
              content: 'Si tengo alguna otra novedad te comento. Gracias!',
              received: true,
              date: '10:20 AM'
            }
          ]
        },
        {
          id: 2,
          name: 'Micaela Alvarez',
          role: 'Marketing Manager',
          avatar: avatar1,
          messages: [
            {
              content: 'Hola John! Entre qué horarios podrías hoy tener la meeting?',
              received: true,
              date: '9:45 AM'
            },
            {
              content: 'Hola Micaela! Muy bien. Yo puedo de 10 a 17 hs.',
              received: false,
              date: '10:05 AM'
            },
            {
              content: 'Dale, agendé la meeting para hoy a las 14hs.',
              received: true,
              date: '10:15 AM'
            }
          ]
        },
        {
          id: 3,
          name: 'Manuel Hoffman',
          role: 'Business Manager',
          avatar: avatar3,
          messages: [
            {
              content: 'Gracias por la reunión de ayer, Manu, fue muy productiva!',
              received: false,
              date: '9:35 AM'
            },
            {
              content: 'Gracias a vos!',
              received: true,
              date: '9:37 AM'
            }
          ]
        }
      ])

And I want to modify it only by adding more items within the messages key of each object, leaving the rest of the state just as it was.

For example, lets say I add two new messages to the first object. The state should look like this:

const [activeChats, setActiveChats] = useState([
    {
      id: 1,
      name: 'Luciana Gutierrez',
      role: 'HR Manager',
      avatar: avatar2,
      messages: [
        {
          content: 'Hola Luciana! Tuviste alguna novedad?',
          received: false,
          date: '9:45 AM'
        },
        {
          content: 'Hola John! Todavía no...',
          received: true,
          date: '10:19 AM'
        },
        {
          content: 'Si tengo alguna otra novedad te comento. Gracias!',
          received: true,
          date: '10:20 AM'
        },
        {
          content: 'Example1',
          received: true,
          date: '10:21 AM'
        },
        {
          content: 'Example2',
          received: true,
          date: '10:22 AM'
        }
      ]
    },
    {
      id: 2,
      name: 'Micaela Alvarez',
      role: 'Marketing Manager',
      avatar: avatar1,
      messages: [
        {
          content: 'Hola John! Entre qué horarios podrías hoy tener la meeting?',
          received: true,
          date: '9:45 AM'
        },
        {
          content: 'Hola Micaela! Muy bien. Yo puedo de 10 a 17 hs.',
          received: false,
          date: '10:05 AM'
        },
        {
          content: 'Dale, agendé la meeting para hoy a las 14hs.',
          received: true,
          date: '10:15 AM'
        }
      ]
    },
    {
      id: 3,
      name: 'Manuel Hoffman',
      role: 'Business Manager',
      avatar: avatar3,
      messages: [
        {
          content: 'Gracias por la reunión de ayer, Manu, fue muy productiva!',
          received: false,
          date: '9:35 AM'
        },
        {
          content: 'Gracias a vos!',
          received: true,
          date: '9:37 AM'
        }
      ]
    }
  ])

How can I do this? Im thinking about the spread operator but I'm not sure how to use it with the nesting I have.

pilchard · Accepted Answer · 2021-07-09 22:41:15Z

2

You need to return a new array for setActiveStates being particularly careful not to mutate the nested object that you are updating. A long hand approach is to findIndex() of the item you want to update, then use this index to spread slice()s of the array before and after the item in question, and also retrieve and clone the item itself and any nested object properties to return a copy.

const newMessages = [{ content: 'new1', received: true, date: '10:21 AM' }, { content: 'new2', received: true, date: '10:22 AM' }];
const itemId = 1;

setActiveChats(prevState => {
  const index = prevState.findIndex(({ id }) => id = itemId);
  const item = prevState[index];
  return [
    ...prevState.slice(0, index),
    { ...item, messages: [...item.messages, ...newMessages] },
    ...prevState.slice(index + 1)
  ];
});

answered Jul 9, 2021 at 22:41

pilchard

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Sam Gomena · Accepted Answer · 2021-07-09 22:45:35Z

2

It's a little bit tedious to do this with nested structures but something like this should work:

    setActiveChats(
      activeChats.map((activeChat, idx) => {
        // Add to the first entry
        if (idx === 0) {
          return {
            ...activeChat,
            // assumes `newMessages` is an array of new messages
            messages: [...activeChat.messages, ...newMessages]
          };
        }
        return activeChat;
      })
    );

See a full working example here.

answered Jul 9, 2021 at 22:45

Sam Gomena

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