js 实现json数组集合去重，差集，并集，交集。

      let list = [
        {
          id: "1",
          content: "A"
        },
        {
          id: "2",
          content: "B"
        },
        {
          id: "3",
          content: "C"
        },
        {
          id: "4",
          content: "D"
        }
      ];
      let arr = [
        {
          id: "1",
          content: "C"
        },
        {
          id: "2",
          content: "D"
        }
      ];

      // let list = [1, 2, 3, 4, 5];
      // let arr = [3, 4];

      // 去重
      function listRemoveRepeat(x) {
        let result = [];
        for (let i = 0; i < x.length; i++) {
          let flag = true;
          let temp = x[i];
          for (let j = 0; j < result.length; j++) {
            // 普通数组 (temp === result[j])
            if (temp.id === result[j].id) {
              flag = false;
              break;
            }
          }
          if (flag) {
            result.push(temp);
          }
        }
        return result;
      }
      // 差集
      function listDifference(x, y) {
        let clone = x.slice(0);
        for (let i = 0; i < y.length; i++) {
          let temp = y[i];
          for (let j = 0; j < clone.length; j++) {
            // 普通数组 (temp === clone[j])
            if (temp.id === clone[j].id) {
              clone.splice(j, 1);
            }
          }
        }
        return listRemoveRepeat(clone);
      }
      // 并集
      function listConcat(x, y) {
        return listRemoveRepeat(x.concat(y));
      }
      // 交集
      function listIntersection(x, y) {
        let result = [];
        for (let i = 0; i < y.length; i++) {
          let temp = y[i];
          for (let j = 0; j < x.length; j++) {
            // 普通数组 (temp === clone[j])
            if (temp.id === x[j].id) {
              result.push(temp);
              break;
            }
          }
        }
        return listRemoveRepeat(result);
      }
      console.log("去重", listRemoveRepeat(list));
      console.log("差集", listDifference(list, arr));
      console.log("并集", listConcat(list, arr));
      console.log("交集", listIntersection(list, arr));