js double forループのネスト、arr2のグループとIDがarr1の属性値と同じであるデータを見つけて、それを新しい配列に追加します
let arr1 = [{group: 1, id: 2, name: "aa"}, {group: 2, id: 1, name: "bb"}, {group: 2, id: 2, name: "cc"}, {group: 3, id: 2, name: "dd"}];
let arr2 = [{group: 1, id: 1, name: "ee"}, {group: 2, id: 2, name: "ff"}, {group: 3, id: 3, name: "gg"}, {group: 4, id: 2, name: "hh"}];
let arr3 = [];
for (let i = 0; i < arr1.length; i++) {
let pre = arr1[i];
for (let j = 0; j < arr2.length; j++) {
let old = arr2[j];
if (pre.group == old.group && pre.id == old.id) {
arr3.push(old);
}
}
}
console.log(arr3);