Не добавлять не уникальный обьект в массив

let fruits = [ 
  { Id: 1, Name: 'Apple' },  
  { Id: 2, Name: 'Pear' }, 
  { Id: 3, Name: 'Orange' },  
  { Id: 4, Name: 'Plum' },  
  { Id: 5, Name: 'Cherry' } 
]; 
let selected = [{Id: 3, Name: 'Orange'}]; 
 
function addUniqueIds(src, dst) { 
  var lookup = {}; 
  for (var i = 0; i < dst.length; i++) { 
    lookup[dst[i].Id] = true; 
  }   
  for (var i = 0; i < src.length; i++) { 
    if (!lookup[src[i].Id]) { 
      lookup[src[i].Id] = true; 
      dst.push(src[i]); 
    } 
  } 
} 
 
addUniqueIds(fruits, selected); 
console.log(selected.length, selected);

const fruits = [{Id: 1, Name: 'Apple'}, {Id: 2, Name: 'Pear'}, { Id: 3, Name: 'Orange'}, { Id: 4, Name: 'Plum'}, { Id: 5, Name: 'Cherry'}]; 
 
const selected = [{Id: 3, Name: 'Orange'}]; 
 
const newSelect = selected.map((item) => JSON.stringify(item)); 
 
const result = fruits.reduce((acc, item) => { 
  if(!newSelect.includes(JSON.stringify(item))) { 
    return acc.concat(item); 
  } 
  return acc; 
}, selected) 
 
console.log(result)

const fruits = [{Id: 1, Name: 'Apple'}, {Id: 2, Name: 'Pear'}, { Id: 3, Name: 'Orange'}, { Id: 4, Name: 'Plum'}, { Id: 5, Name: 'Cherry'}]; 
 
const selected = [{Name: 'Orange', Id: 3}, {Name: 'Pear', Id: 2}]; 
 
const newSelect = selected.map((item) => (item.Id)); 
 
const result = fruits.reduce((acc, item) => { 
  if(!newSelect.includes(item.Id)) { 
    return acc.concat(item); 
  } 
  return acc; 
}, selected) 
 
console.log(result)