在分配变量之前，如何检查未定义
我使用查找方法提取ID（字符串），但这是由于不存在而返回的未定义。
const additionalLinePhoneNumber = products.find(product => product.name === 'segundaLinea').id;
产品具有以下内容：
(2) [ProductInventoryList, ProductInventoryList]
0: ProductInventoryList {_id: "12345", _name: "lineaFija", _productInventoryCharacteristics: ProductInventoryCharacteristics}
1: ProductInventoryList {_id: "12345", _name: "primeraLinea", _productInventoryCharacteristics: ProductInventoryCharacteristics}
length: 2
因此，“ segundalinea”不会返回，因此发现给我以下错误：
错误错误：und offield（在Promise）：TypeError：无法读取未定义的属性'ID' TypeError：无法读取未定义的属性
我尝试这样做的属性“ ID”：
const additionalLinePhoneNumber = products.find(product => product.name === 'segundaLinea').id ? undefined : '';
我缺少什么？
在下面尝试尝试：
Im using a find method to extract an ID (string) but this is returning an undefined as it doesnt exist.
const additionalLinePhoneNumber = products.find(product => product.name === 'segundaLinea').id;
Products has the following:
(2) [ProductInventoryList, ProductInventoryList]
0: ProductInventoryList {_id: "12345", _name: "lineaFija", _productInventoryCharacteristics: ProductInventoryCharacteristics}
1: ProductInventoryList {_id: "12345", _name: "primeraLinea", _productInventoryCharacteristics: ProductInventoryCharacteristics}
length: 2
So "segundaLinea" isnt returned so the find gives me the following error:
ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'id' of undefined
TypeError: Cannot read property 'id' of undefined
I tried doing this but doesnt work:
const additionalLinePhoneNumber = products.find(product => product.name === 'segundaLinea').id ? undefined : '';
What am I missing?
Trying the awnser below:
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您可以使用
编辑：
对于打字稿，使用版本3.7 添加了对可选链接的支持。如果您无法更新版本，则必须在多行上进行操作：
如果您必须执行几次，则可能应该写一个助手功能。
You can use optional chaining like this:
Edit:
For Typescript, the support for optional chaining was added with the version 3.7. If you can't update your version you have to do it on multiple lines:
If you have to do this several times, you should probably write a helper function.
如果您不想更新，只需使用可选（？）链接
if you don't want to update, simply use optional(?) chaining