replace an object inside an array with reducer

Question

i want to replace an object inside an array of object using id to find it, the payload has the new object

const initialState = {
  allComments: []
};

case LIKE_COMMENT:
      let index = state.allComments.findIndex(
        value => value._id === payload._id
      );
      if (index === -1) {
        return {
          ...state,
          allComments: [...state.allComments, ...payload]
        };
      } else {
        return {
          ...state,
          allComments: [
            (state.allComments[index] = payload),
            ...state.allComments
          ]
        };
      }

them problem that it keep pushing that object without replacing the previous one

fila90 · Accepted Answer · 2020-02-14 00:02:27Z

2

 case LIKE_COMMENT:
      return {
        ...state,
        allComments: state.allComments.map(comment => {
          if (comment.id === payload._id) return payload;
          return comment;
        })
      }

this will replace comment with payload and return all other comments

answered Feb 14, 2020 at 0:02

fila90

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Comments

Seth Lutske · Accepted Answer · 2020-02-14 00:02:55Z

1

I think you actually need to define a new array based on your old one before returning it into your state:

... else {
  newComments = state.allComments
  newComments[index] = payload
  return {
    ...state,
    newComments
  };
}

answered Feb 14, 2020 at 0:02

Seth Lutske

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Comments

Đinh Carabus · Accepted Answer · 2020-02-14 00:05:35Z

1

You can use map to create a shallow copy of the allComments array where the matching index is replaced by the payload:

case LIKE_COMMENT:
    return {
      ...state,
      allComments: state.allComments.map(c => c._id === payload._id ? payload : c)
    };

answered Feb 14, 2020 at 0:05

Đinh Carabus

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2 Comments

Buk Lau Over a year ago

thank you i get it , i thought if i did replace that index i can use it right away .

Đinh Carabus Over a year ago

allComments: [ (state.allComments[index] = payload), ...state.allComments ] replaces the object at the specified index but it also adds the payload object as the first item of the array. It is interpreted as [ payload, ...allComments ]

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