将数组合并到对象中会给出未定义的

var obj = {};
var arr = [1, 2, 3];

for (var i = 0; i < arr.length; i++) {
  obj[i] = arr[i];
}

console.log(obj); // 输出：{0: 1, 1: 2, 2: 3}

var arr = [1, 2, 3];

var obj = arr.reduce(function(acc, curr, index) {
  acc[index] = curr;
  return acc;
}, {});

console.log(obj); // 输出：{0: 1, 1: 2, 2: 3}

var obj = {};
var arr = [1, 2, 3];

Object.assign(obj, arr);

console.log(obj); // 输出：{0: 1, 1: 2, 2: 3}