let arr1 = [
        { type:1, name:"", age:"", num:"a" },
        { type:2, name:"", age:"", num:"b" },
        { type:3, name:"", age:"", num:"c" },
        { type:4, name:"", age:"", num:"d" }
];
let arr2 = [
        { type:1, name:"1", age:"45" },
        { type:3, name:"2", age:"4" },
        { type:2, name:"4", age:"4" },
        { type:4, name:"5", age:"4" }
      ];
      
  // 根据 type属性对应，最终合并成
let endArr = [
    { type:1, name:"1", age:"45",num:"a" },
    { type:2, name:"2", age:"4", num:"b" },
    { type:3, name:"4", age:"4", num:"c" },
    { type:4, name:"5", age:"4", num:"d" }
]

我的思路，先把两个数组合成一个，变成一个分组问题，然后对同一组进行合并，最后对每一组的属性值进行重新赋值；