how to get 4 unique values from array of object in javascript code example

Example 1: filter array with unique objects javascript

const array =
  [
    { "name": "Joe", "age": 17 },
    { "name": "Bob", "age": 17 },
    { "name": "Carl", "age": 35 }
  ]

const key = 'age';

const arrayUniqueByKey = [...new Map(array.map(item =>
  [item[key], item])).values()];

console.log(arrayUniqueByKey);

   /*OUTPUT
       [
        { "name": "Bob", "age": 17 },
        { "name": "Carl", "age": 35 }
       ]
   */

 // Note: this will pick the last duplicated item in the list.

Example 2: javascript map return array with distinc values

//ES6
let array = [
  { "name": "Joe", "age": 17 },
  { "name": "Bob", "age": 17 },
  { "name": "Carl", "age": 35 }
];
array.map(item => item.age)
  .filter((value, index, self) => self.indexOf(value) === index)

> [17, 35]

Example 3: javascript get unique values from key

const unique = [...new Set(array.map(item => item.age))];

Example 4: get only unique values from array javascript

arr = [2, 2, 2, 1, 3, 3, 3,3, 4, 5];
arr = arr.sort().filter((item,i)=>!(arr[i] == arr[i+1] || arr[i-1]==arr[i]));
// this will remove all item which are repeating more then one
console.log(arr);
// [1, 4, 5]