Javascript 承诺解决后打字稿返回布尔值
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Typescript returning boolean after promise resolved
提问by user2473015
I'm trying to return a boolean after a promise resolves but typescript gives an error saying
我试图在承诺解决后返回一个布尔值，但打字稿给出了一个错误说
A 'get' accessor must return a value.
A 'get' accessor must return a value.
my code looks like.
我的代码看起来像。
get tokenValid(): boolean {
// Check if current time is past access token's expiration
this.storage.get('expires_at').then((expiresAt) => {
return Date.now() < expiresAt;
}).catch((err) => { return false });
}
This code is for Ionic 3 Application and the storage is Ionic Storage instance.
此代码用于 Ionic 3 应用程序，存储为 Ionic Storage 实例。
回答by Shaun Luttin
You can return a Promisethat resolves to a boolean like this:
您可以返回Promise解析为布尔值的a ，如下所示：
get tokenValid(): Promise<boolean> {
// |
// |----- Note this additional return statement.
// v
return this.storage.get('expires_at')
.then((expiresAt) => {
return Date.now() < expiresAt;
})
.catch((err) => {
return false;
});
}
The code in your question only has two return statements: one inside the Promise's thenhandler and one inside its catchhandler. We added a third return statement inside the tokenValid()accessor, because the accessor needs to return something too.
您问题中的代码只有两个 return 语句：一个在 Promise 的then处理程序中，一个在其catch处理程序中。我们在访问器中添加了第三个 return 语句tokenValid()，因为访问器也需要返回一些东西。
Here is a working example in the TypeScript playground:
这是TypeScript 游乐场中的一个工作示例：
class StorageManager {
// stub out storage for the demo
private storage = {
get: (prop: string): Promise<any> => {
return Promise.resolve(Date.now() + 86400000);
}
};
get tokenValid(): Promise<boolean> {
return this.storage.get('expires_at')
.then((expiresAt) => {
return Date.now() < expiresAt;
})
.catch((err) => {
return false;
});
}
}
const manager = new StorageManager();
manager.tokenValid.then((result) => {
window.alert(result); // true
});
回答by Mankeomorakort
Your function should be:
你的功能应该是：
get tokenValid(): Promise<Boolean> {
return new Promise((resolve, reject) => {
this.storage.get('expires_at')
.then((expiresAt) => {
resolve(Date.now() < expiresAt);
})
.catch((err) => {
reject(false);
});
});
}
