javascript - 如果 Javascript 中缺少对象键，则跳过未定义错误

Question

我想知道如果缺少键，我们如何跳过抛出未定义的错误。

[
  {
    "id": "foo1",
    "name": "Test1",
    "description": "random test1",
    "languages": [
      "en"
    ],
    "subThemes": [
      {
        "id": "1",
        "name": "Bike"
      },
      {
        "id": "2",
        "name": "Testy",
        "description": "Testing this thing1"
      }
    ]
  },
  {
    "id": "foo2",
    "name": "Test",
    "description": "random test2",
    "languages": [
      "en"
    ],
    "subThemes": [
      {
        "id": "3",
        "name": "Bike2"
      },
      {
        "id": "4",
        "name": "Testy2",
        "description": "Testing this thing2"
      }
    ]
  },
  {
    "id": "foo3",
    "name": "Test3",
    "description": "random test3",
    "languages": [
      "en"
    ]
  }
]

假设我有一个像上面这样的数组对象，如果我在它上面做一个映射，它会给我一个错误，因为我在第三个对象中没有 subThemes 键。

const children = theme.subThemes
      .map(subTheme => {
        const { subThemes = [] } = aggregations;  
              ...rest of the code}

TypeError: Cannot read property 'map' of undefined

如何绕过未定义的错误？提前致谢。

标签： javascriptjsonreactjs

Answer 1

听起来怎么样？

if ( Array.isArray(myJson.languages))
     myJson.languages.map(.....

或返回空数组（ES6 语法）

(myJson.languages || []).map(x => { .... });

或返回 undefined 而没有错误（ES6 语法）

myJson.languages?.map(x => { ... });