对于数组中的每个元素，如果存在与之相等的元素，则将其标记为“待移除”，同时移除相等的元素。i元素在最后被移除。

function removeDuplicates(a){
  for(let i = 0 ; i < a.length ; i++){
    let toRemove = false;
    for(let j = 0; j < a.length ; j++){
      if(i != j && a[i].id == a[j].id){
        toRemove = true;
        a.splice(j,1);
      }
    }
    if(toRemove) a.splice(i,1)
  }
  return a;
}

这是另一种方法

let data = 
[
{id: 4, country: "Japan"},
{id: 5, country: "Korea"},
{id: 6, country: "Philippines"},
{id: 6, country: "Philippines"}

]; 

data.map((s, i) => {
 if (i>0 &&s.id != data[i- 1].id) {
  return s;
 }else{
  delete data[i- 1];
 }
});

const data = [
    {id: 4, country: 'Japan'},
    {id: 5, country: 'Korea'},
    {id: 6, country: 'Philippines'},
    {id: 6, country: 'Philippines'}
];

const duplicates = data.filter((obj, index, arr) => {
  return arr.map(mapObj => mapObj.id).indexOf(obj.id) !== index;
});

const uniqueData = data.filter((obj, index, arr) => {
  return arr.map(mapObj => mapObj.id).indexOf(obj.id) === index;
});

console.log("Duplicates:", duplicates);
console.log("Unique data:", uniqueData);