应用地图功能有效，而 foreach 功能不起作用

Question

我有一个反应应用程序，它使用 map 函数显示嵌套 json 中的项目，但是其中一个类别可能是空的，这会使整个应用程序崩溃，我已经使用每个函数的 js 测试了相同 json 的 foreach 函数，它完美运行，我正在尝试翻译相同的逻辑来解决空类别问题。

这是我在同一个 json 上的每个测试，但带有列表：

测试1

let obj = {
  "name": "Menu",
  "children": [
    {
      "type": "category",
      "name": "Burgers",
      "children": [
        {
          "type": "item",
          "name": "Burger 1",
          "children": [
            {
              "type": "modifier",
              "name": "Promo",
              "children": [
                {
                  "type": "item",
                  "name": "Promo 1"
                }
              ]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [
                {
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [
                {
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Tomato"
                },
                {
                  "type": "ingredient",
                  "name": "Pickles"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Burger 2",
          "children": [
            {
              "type": "modifier",
              "name": "Promo",
              "children": [
                {
                  "type": "item",
                  "name": "Promo 1"
                }
              ]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [
                {
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [
                {
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Tomato"
                },
                {
                  "type": "ingredient",
                  "name": "Pickles"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Coming Soon Offers"
        }
      ]
    },
    {
      "type": "category",
      "name": "Pizzas",
      "children": [
        {
          "type": "item",
          "name": "Pizza 1",
          "children": [
            {
              "type": "modifier",
              "name": "Promo",
              "children": [
                {
                  "type": "item",
                  "name": "Promo 1"
                }
              ]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [
                {
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [
                {
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Mashrooms"
                },
                {
                  "type": "ingredient",
                  "name": "Olives"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Pizza 2",
          "children": [
            {
              "type": "modifier",
              "name": "Promo",
              "children": [
                {
                  "type": "item",
                  "name": "Promo 1"
                }
              ]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [
                {
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [
                {
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Mashrooms"
                },
                {
                  "type": "ingredient",
                  "name": "Olives"
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}
let body = document.querySelector('body');
function print(obj){
  let str = `<li>${obj.name}</li>`;
  if(obj.children){
    str += '<ul>' 
    for(let c of obj.children) str += print(c)
    str += '</ul>'
  }
  return str;
}
document.body.innerHTML = print(obj);

测试 2

const buildMenu = (data) => {
  let ul = document.createElement('ul');
  data.children.forEach(i => {
    let li = document.createElement('li');
    li.innerText = i.name;
    li.className = i.type;
    if (i.children) li.appendChild(buildMenu(i));
    ul.appendChild(li);
  });

  return ul;
};

let data = {

  "name": "Menu",
  "children": [{
      "type": "category",
      "name": "Burgers",
      "children": [{
          "type": "item",
          "name": "Burger 1",
          "children": [{
              "type": "modifier",
              "name": "Promo",
              "children": [{
                "type": "item",
                "name": "Promo 1"
              }]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [{
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [{
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Tomato"
                },
                {
                  "type": "ingredient",
                  "name": "Pickles"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Burger 2",
          "children": [{
              "type": "modifier",
              "name": "Promo",
              "children": [{
                "type": "item",
                "name": "Promo 1"
              }]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [{
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [{
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Tomato"
                },
                {
                  "type": "ingredient",
                  "name": "Pickles"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Coming Soon Offers"
        }
      ]
    },
    {
      "type": "category",
      "name": "Pizzas",
      "children": [{
          "type": "item",
          "name": "Pizza 1",
          "children": [{
              "type": "modifier",
              "name": "Promo",
              "children": [{
                "type": "item",
                "name": "Promo 1"
              }]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [{
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [{
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Mashrooms"
                },
                {
                  "type": "ingredient",
                  "name": "Olives"
                }
              ]
            }
          ]
        },
        {
          "type": "item",
          "name": "Pizza 2",
          "children": [{
              "type": "modifier",
              "name": "Promo",
              "children": [{
                "type": "item",
                "name": "Promo 1"
              }]
            },
            {
              "type": "group",
              "name": "Drinks",
              "children": [{
                  "type": "item",
                  "name": "Coke"
                },
                {
                  "type": "item",
                  "name": "Light Coke"
                },
                {
                  "type": "item",
                  "name": "Sprite"
                },
                {
                  "type": "item",
                  "name": "Fanta"
                }
              ]
            },
            {
              "type": "modifier",
              "name": "Without",
              "children": [{
                  "type": "ingredient",
                  "name": "Onion"
                },
                {
                  "type": "ingredient",
                  "name": "Mashrooms"
                },
                {
                  "type": "ingredient",
                  "name": "Olives"
                }
              ]
            }
          ]
        }
      ]
    }
  ]
};

document.body.appendChild(buildMenu(data));

Answer 1

您在多个地方缺少对象空检查。

1. 在您的ItemList 组件的渲染函数中有一个 else 语句，您可以在其中分配 selectedChild 和 selectedItem。您需要检查 activelist.children 和 selectedChild.children 是否为空

   const selectedChild = activelist.children.length ? activelist.children[this.state.selected] : null;
   const selectedItem = selectedChild.children && selectedChild.children.length
        ? selectedChild.children[this.state.itemSelected]: null;

1. 要渲染 selectedChild，您应该检查 children 是否为空。

{
  selectedChild &&
  selectedChild.children &&
  selectedChild.children.length &&
  selectedChild.children.map(
    (item, index) => (
      <Item
        className="person"
        key={index}
        Title={item.name}
        onClick={this.handleClick}
        index={index}
      />
   )
)}

1. 要渲染 selectedItem，您应该检查 children 是否为空

<div>
  { selectedItem &&
    selectedItem.children &&
    selectedItem.children.map((item, index) => (
      <Modifiers
        key={index}
        title={item.name}
        myKey={index}
        options={item.children}
        childk={item.id}
       />
     ))
  }
</div>
<div>
  { 
    selectedItem &&
    selectedItem.size &&
    (<div>
        <Size
           options={selectedItem.size}
           sizetitle={"Size"}
        />
       </div>)
   }
</div>