how to get last object from array and remains parent array same in javascript

Question

Hi I have an array with a messages key which have multiple objects, i want to remove all objects except the last object in the messages array

I have example array below :

const array = [
    {
      messages: [
        { content: "abc", id: "message01" },
        { content: "def", id: "message02" },
        { content: "ghi", id: "message03" }
      ],
      user: "user 1",
      participants: ["user1", "user2"],
      id: "chat01"
    },
    {
      messages: [
        { content: "hello", id: "message01" },
        { content: "hi", id: "message02" },
        { content: "How are you", id: "message03" }
      ],
      user: "user 2",
      participants: ["user1", "user2"],
      id: "chat02"
    }
  ];

my excepted array below:

const expectedArray = [
    {
      messages: [{ content: "ghi", id: "message03" }],
      user: "user 1",
      participants: ["user1", "user2"],
      id: "chat01"
    },
    {
      messages: [{ content: "How are you", id: "message03" }],
      user: "user 2",
      participants: ["user1", "user2"],
      id: "chat02"
    }
  ];

i am unable to remove other objects from the messages array, except last object — Manohar Pamishetty
– Manohar Pamishetty, Commented Jan 27, 2022 at 14:03

Sarout · Accepted Answer · 2022-01-27 14:15:46Z

3

Is this what you want?

EDIT: this code will loop the array, and set messages to messages[0] which is the last object

const array = [
  {
    messages: [
      {
        content: "abc",
        id: "message01"
      },
      {
        content: "def",
        id: "message02"
      },
      {
        content: "ghi",
        id: "message03"
      }
    ],
    user: "user 1",
    participants: ["user1", "user2"],
    id: "chat01"
  },
  {
    messages: [
      {
        content: "hello",
        id: "message01"
      },
      {
        content: "hi",
        id: "message02"
      },
      {
        content: "How are you",
        id: "message03"
      }
    ],
    user: "user 2",
    participants: ["user1", "user2"],
    id: "chat02"
  }
];

array.forEach(e=>{
  e.messages = e.messages[e.messages.length - 1]
})

console.log(array)

edited Jan 27, 2022 at 14:15

answered Jan 27, 2022 at 14:05

Sarout

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5 Comments

Giovanni Esposito Over a year ago

While your answer could be correct, write a brief description of what your code does is always a good idea. Code-only answer are usually downvoted (a claer example here stackoverflow.com/a/70876176/13897065 in which you wrote the correct answer that is downvoted). Just a suggestion. Have a nice coding =)

Sarout Over a year ago

thank you so much, it will help me to help others, it's a great idea BTW, I'm editing it right now, but also don't forget this is my first week in stackoverflow

Sarout Over a year ago

@ManoharPamishetty you're welcome dear, but please if it solves your issue please mark it as accepted so other visitors know that this is the solution of your issue

matzar Over a year ago

Nice @Sarout. To get the last element of the array, you could also use in your array.forEach loop instead of e.messages[e.messages.length - 1]: e.messages.pop(), e.messages.slice(-1).pop(), e.messages.slice(-1)[0]

matzar Over a year ago

source on how to get the last element of the array: w3docs.com/snippets/javascript/…

Balint · Accepted Answer · 2022-01-27 14:20:14Z

1

const array = [
    {
      messages: [
        { content: "abc", id: "message01" },
        { content: "def", id: "message02" },
        { content: "ghi", id: "message03" }
      ],
      user: "user 1",
      participants: ["user1", "user2"],
      id: "chat01"
    },
    {
      messages: [
        { content: "hello", id: "message01" },
        { content: "hi", id: "message02" },
        { content: "How are you", id: "message03" }
      ],
      user: "user 2",
      participants: ["user1", "user2"],
      id: "chat02"
    }
  ];
  
  for (let i = 0; i < array.length; i++) {
    array[i].messages = new Array (array[i].messages[array[i].messages.length -1])
}

  
  console.log (array)

answered Jan 27, 2022 at 14:20

Balint

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Comments

matzar · Accepted Answer · 2022-01-27 14:56:31Z

const array = [
    {
      messages: [
        { content: "abc", id: "message01" },
        { content: "def", id: "message02" },
        { content: "ghi", id: "message03" }
      ],
      user: "user 1",
      participants: ["user1", "user2"],
      id: "chat01"
    },
    {
      messages: [
        { content: "hello", id: "message01" },
        { content: "hi", id: "message02" },
        { content: "How are you", id: "message03" }
      ],
      user: "user 2",
      participants: ["user1", "user2"],
      id: "chat02"
    }
  ];
  

/** slice() method gets the last element of the array. 
If we provide negative index -1 to it
then it will remove the last item and
return it as a new array.
We overwrite messages array with the
return value of the slice() method which
is a new array containing only the last
element of the original messages array.
*/
array.forEach(e => e.messages = e.messages.slice(-1))

console.log(array)

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