'string' 仅指一种类型，但在这里被用作值

Question

TypeScript 新手。我正在尝试设置状态但收到此错误。

错误：'string' only refers to a type, but is being used as a value here.

const state = reactive({
    user: {
        uid: "",
        provider: string[],
    }
});

const user = auth.currentUser;
if (user != null) {
    state.user.uid = user.uid || "";
    user.providerData.forEach(function(profile) {
        state.user.provider.push({
            providerId: profile.providerId,
            uid: profile.uid,
        })
    });
}

Answer 1

仅基于此声明：

const state = reactive({
    user: {
        uid: "",
        provider: string[],
    }
});

您编写它的目的是为provider属性赋予 类型string[]，但在该语句中，它试图设置变量的值（而不是类型），并且由于string[]不是值，因此会引发错误。要将 的值设置provider为类型为 的数组string[]，您可以使用：

const state = reactive({
    user: {
        // initialize as "", type is automatically set to string
        uid: "",

        // create array and override its type to an array of strings
        provider: [] as string[], 
    }
});

然而，当我们看看你如何使用这个state变量时：

const user = auth.currentUser;
if (user != null) {
    state.user.uid = user.uid || "";
    user.providerData.forEach(function(profile) {
        state.user.provider.push({  // <-- this bit here is important
            providerId: profile.providerId,
            uid: profile.uid,
        })
    });
}

在这些行中，您将类型的对象推送到数组{ providerId: string, uid: string }中state.user.provider。这意味着您的第一段代码实际上需要是：

const state = reactive({
    user: {
        // initialize as "", the type is automatically set to string
        uid: "", 

        // create empty array and override its type to an array of { providerId: string, uid: string } objects
        provider: [] as ({ providerId: string, uid: string })[], 
    }
});

您还可以使用接口来命名该对象形状：

interface ProviderData {
  providerId: string;
  uid: string;
}
// you could also use this similar syntax:
// type ProviderData = {
//   providerId: string;
//   uid: string;
// }

const state = reactive({
    user: {
        // initialize as "", the type is automatically set to string
        uid: "", 

        // create empty array and override its type to an array of ProviderData objects
        provider: [] as ProviderData[], 
    }
});