Remove duplicate values and overwrite the array

There is such an array:

[
    { message: '12949', author: 'esP' },
    { message: '1609', author: 'user' },
    { message: '1613', author: 'adm' },
    { message: '12949', author: 'Mdr' },
    { message: '12949', author: 'rood' }
]

How can you make sure that messages are not repeated, the authors are written separated by commas:

[
    { message: '12949', author: 'esP, Mdr, rood' },
    { message: '1609', author: 'user' },
    { message: '1613', author: 'adm' }
]

I check for uniqueness this way:

const _ = require('underscore');
let a = _.uniq(arr, x => x.message)

What to do next? Create a second loop and compare values?

>Solution :

We can use Array.reduce(), to get the required result.

We’d add each item to a map object (accumulator), using the message value as the key, then use Object.values() to return our desired result array:

const arr = [ { message: '12949', author: 'esP' }, { message: '1609', author: 'user' }, { message: '1613', author: 'adm' }, { message: '12949', author: 'Mdr' }, { message: '12949', author: 'rood' } ];

const result = Object.values(arr.reduce((acc, { message, author }) => { 
    if (!acc[message]) {
        acc[message] = { message, author };
    } else {
        acc[message].author += `, ${author}`;
    }
    return acc;
}, {}));

console.log('Result:', result)

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