英文:
Cannot invoke value of map because possibly undefined
问题
以下是您要翻译的代码部分：
在我的应用程序中，我有一个`Map`，它以用户角色作为键返回一组设置。
enum Role {
ROLE_1 = "role"
}
const settingsRole1 = {}
const defaultSettings = {}
const secondParameter = ""
const map = new Map<Role, any>([
[Role.ROLE_1, settingsRole1]
]);
const settings = map.get(Role.ROLE_1) ?? defaultSettings;
现在我想引入第二个参数。由于我希望尽量少修改代码，我想将`Map<Role，Settings>`转换为`Map<Role，(secondParameter: string) => Settings>`，从映射中返回一个函数，稍后将调用它。
enum Role {
ROLE_1 = "role"
}
const settingsRole1 = {}
const defaultSettings = {}
const secondParameter = ""
const map = new Map<Role, (secondParameter: string) => any>([
[Role.ROLE_1, (secondParameter: string) => settingsRole1]
]);
const settings = map.get(Role.ROLE_1)(secondParameter) ?? defaultSettings;
尝试调用从映射返回的函数时，我收到以下错误：`TS2722：无法调用可能为'undefined'的对象`。
我尝试了一下保护它，但似乎不起作用...
enum Role {
ROLE_1 = "role"
}
const settings = {}
const defaultSettings = {}
const map = new Map<Role, (secondParameter: string) => any>([
[Role.ROLE_1, (secondParameter: string) => settings]
]);
const settings = map.has(Role.ROLE_1) ? map.get(Role.ROLE_1)(secondParameter) : defaultSettings;
我不明白如何使保护工作，无论如何，如果您想建议一种方法，我会考虑尝试其他方法。
请注意，我只提供了代码的翻译，不包括问题或其他内容。
英文:
In my application I have a Map that returns a set of settings taking the role of the user as a key.
enum Role {
ROLE_1 = "role"
}
const settingsRole1 = {}
const defaultSettings = {}
const secondParameter = ""
const map = new Map<Role, any>([
[Role.ROLE_1, settingsRole1]
]);
const settings = map.get(Role.ROLE_1) ?? defaultSettings;
Now I want to introduce a second parameters. Since I want to modify the code as little as possible, I thought to transform the Map<Role, Settings> into Map<Role, (secondParameter: string) => Settings>, returning a function from the map, that will be invoked later.
enum Role {
ROLE_1 = "role"
}
const settingsRole1 = {}
const defaultSettings = {}
const secondParameter = ""
const map = new Map<Role, (secondParameter: string) => any>([
[Role.ROLE_1, (secondParameter: string) => settingsRole1]
]);
const settings = map.get(Role.ROLE_1)(secondParameter) ?? defaultSettings;
I receive this error while trying to calling the function returning from the map: TS2722: Cannot invoke an object which is possibly 'undefined'.
I tried to guard it, but it doesn't seem to work...
enum Role {
ROLE_1 = "role"
}
const settings = {}
const defaultSettings = {}
const map = new Map<Role, (secondParameter: string) => any>([
[Role.ROLE_1, (secondParameter: string) => settings]
]);
const settings = map.has(Role.ROLE_1) ? map.get(Role.ROLE_1)(secondParameter) : defaultSettings;
I don't understand how to make the guard work, anyways I would consider trying other approaches if you want to suggest one
答案1
得分: 0
使用 ! 在表达式后告诉编译器忽略其可为 null 的特性。在你的情况下，应该是（带有显式键检查）
const settings = map.has(Role.ROLE_1) ? map.get(Role.ROLE_1)!(secondParameter) : defaultSettings;
另一种方法是使用可选链 ?. 运算符
const settings = map.get(Role.ROLE_1)?.(secondParameter) ?? defaultSettings;
但从语义上稍有不同 - 它不区分丢失的键和具有显式 null / undefined 值的键。
英文:
Use ! after expression to tell compiler to ignore its nullability. In your case it should be (with explicit key check)
const settings = map.has(Role.ROLE_1) ? map.get(Role.ROLE_1)!(secondParameter) : defaultSettings;
Alternative way is to use optional chaining ?. operator
const settings = map.get(Role.ROLE_1)?.(secondParameter) ?? defaultSettings;
but it's slightly different semantically - it doesn't distinguish between missing keys and keys with explicit null / undefined values.
答案2
得分: 0
你可以使用可选链 ?. 来访问第一个参数。
const settings = map.get(Role.ROLE_1)?.(secondParameter) ?? defaultSettings;
英文:
You can use optional chaining ?. for first parameter
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
const settings = map.get(Role.ROLE_1)?.(secondParameter) ?? defaultSettings;
<!-- end snippet -->
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