js如何改变数组对象中某一个属性

```javascript
// 怎么能只把a中b的值，按顺序替换成f中d的值，c值不变
  var a = [
      {b:1,c:5},
      {b:2,c:6},
      {b:3,c:7},
      {b:4,c:8},
      ]

     var f =[
      {d:12},
      {d:13},
      {d:14},
      {d:15},
     ]

```

题主要的代码如下，有帮助麻烦点个采纳【本回答右上角】，谢谢~~

<script>
// 怎么能只把a中b的值，按顺序替换成f中d的值，c值不变
  var a = [
      {b:1,c:5},
      {b:2,c:6},
      {b:3,c:7},
      {b:4,c:8},
      ]
     var f =[
      {d:12},
      {d:13},
      {d:14},
      {d:15},
    ]
    a.forEach((item, index) => {
        item.b = f[index].d;
    });
    alert(JSON.stringify(a))
</script>