Change boolean in the filtered array

Question

I have array and i need to write a function that accepts the name of the user and and boolean should be changed to true.

var array = [{
  user: "Sasha",
  message: "Hello guys",
  time: "20:28:2",
  read: false
}, {
  user: "Sasha",
  message: "How are you doing",
  time: "20:28:2",
  read: false
}, {
  user: "Dima",
  message: "I am fine, thanks!",
  time: "20:28:2",
  read: false
}, {
  user: "Katya",
  message: "I am doing well! What about you?",
  time: "20:28:2",
  read: false
}]

function readMessage(user) {
  let test = array
  let filtered = test.filter(item => item.user === user);
  let y = filtered.map(item => item.user && !item.read);
  console.log(y);
}

readMessage();

I think i should filter array, and then change bool to the opposite, but after that map function returns only bools. How to change boolean and push changes to the original array?

Possible duplicate of [Modify object property in an array of objects](https://stackoverflow.com/questions/16691833/modify-object-property-in-an-array-of-objects) — Heretic Monkey, Nov 12 '18 at 18:40
`.map` and `.filter` create copies of the original array, you need to use `for` or `.forEach` and operate on `user` directly if you want to modify the original array — Rob M., Nov 12 '18 at 18:46

score 1 · Answer 1 · answered Nov 12 '18 at 19:06

First you need to filter the array with your desired value, then you get a filtered array, now you map over that array to update the boolean value.

// put your messages array in a variable
var array = [{
  user: "Sasha",
  message: "Hello guys",
  time: "20:28:2",
  read: false
}, {
  user: "Sasha",
  message: "How are you doing",
  time: "20:28:2",
  read: false
}, {
  user: "Dima",
  message: "I am fine, thanks!",
  time: "20:28:2",
  read: false
}, {
  user: "Katya",
  message: "I am doing well! What about you?",
  time: "20:28:2",
  read: false
}]

function readMessage(user) {
  let test = array
  let filtered = test.filter(item => item.user === user);
  // console.log(filtered); // check the filtered array;
  filtered.map(item => item.read = true);
  console.log(filtered);
}
// call the function now;
readMessage('Sasha');

score 0 · Answer 2 · answered Nov 12 '18 at 18:45

This line of code worked but just returns your filtered/mapped values:

array.filter(item => item.user === 'Sasha').map(item => item.read = true)

In your function return the array instead

array.filter(item => item.user === user).map(item => item.read = true)
return array;

score 0 · Answer 3 · answered Nov 12 '18 at 18:46

0

You can just set read to true inside the map function like this:

function readMessage(user){
   let test = array
   let filtered = test.filter(item => item.user === user);
   let y = filtered.map(item => item.read = true);
}

[]'s

answered Nov 12 '18 at 18:46

Denis Marques

110
3

score 0 · Answer 4 · answered Nov 12 '18 at 19:01

This version does not modify your messages in place but only returns the filtered, updated list:

const items = [
  {user: "Sasha", message: "Hello guys", time: "20:28:2", read: false},
  {user: "Sasha", message: "How are you doing", time: "20:28:2", read: false},
  {user: "Dima", message: "I am fine, thanks!", time: "20:28:2", read: false},
  {user: "Katya", message: "I am doing well! What about you?", time: "20:28:2", read: false}
] 

const readMessages = (items, user) => items
  .filter(item => item.user === user)
  .map(({read, ...rest}) => ({...rest, read: !read}))

const updatedItems = readMessages(items, 'Sasha')

console.log(updatedItems)

This version returns a new entire list of messages, with the matching ones changed:

const items = [
  {user: "Sasha", message: "Hello guys", time: "20:28:2", read: false},
  {user: "Sasha", message: "How are you doing", time: "20:28:2", read: false},
  {user: "Dima", message: "I am fine, thanks!", time: "20:28:2", read: false},
  {user: "Katya", message: "I am doing well! What about you?", time: "20:28:2", read: false}
] 

const updatedMessages = (items, userToCheck) => items
  .map(({user, read, ...rest}) => user == userToCheck
      ? {...rest, user, read: !read}
      : {...rest, user, read}
  )

const updatedItems = updatedMessages(items, 'Sasha')

console.log(updatedItems)

And this version updates the list of items in place. (I would recommend against this unless it's absolutely necessary. Immutable data has great benefits!)

const updateMessages = (items, userToCheck) => {
  items.forEach(item => {
    if (item.user == userToCheck) {
      item.read = !item.read
    }
  })
  return items
}

Change boolean in the filtered array

4 Answers4