[英]Typescript type a or type b
I have the 2 following interfaces我有以下 2 个接口
interface IComment extends IData {
comment: string;
}
interface IHistory extends IData{
differences: any[];
timeStamp: number;
}
both of them extend他们都延伸
interface IData {
user: string;
date: Moment | string;
isHistory: boolean;
}
now to the problem现在解决问题
I have an Array with elements of IComment and IHistory.我有一个包含 IComment 和 IHistory 元素的数组。
const data: Array<IHistory | IComment> = [...someHistoryArray, ...someCommentArray]
now when I want to map over the array and I want to access the timeStamp现在当我想映射数组并且我想访问时间戳时
data.map((entry: IHistory | IComment) => {
if(entry.isHistory) {
entry.timeStamp
// TS2339: Property 'timeStamp' does not exist on type 'IHistory | IComment'. Property 'differences' does not exist on type 'IComment'.
} else {
entry.comment
// TS2339: Property 'comment' does not exist on type 'IHistory | IComment'. Property 'comment' does not exist on type 'IHistory'.
}
})
well I found 2 solutions that aren´t satisfing enough for me...好吧,我发现了 2 个对我来说不够满意的解决方案......
I could write at every position我可以在每个位置写作
(entry as IHistory).timeStamp
I could define for example我可以定义例如
const historyEntry: IHistory = entry as IHistory;
Are there any other possible solutions?还有其他可能的解决方案吗?
You can use isHistory
as a discriminant for the union if you add specific definitions in each interface: 如果在每个接口中添加特定的定义,则可以将isHistory
用作联合的判别式:
interface IComment extends IData {
comment: string;
isHistory: false;
}
interface IHistory extends IData {
differences: any[];
timeStamp: number;
isHistory: true;
}
interface IData {
user: string;
date: string;
isHistory: boolean;
}
let data: Array<IComment | IHistory>=[]
data.map((entry: IHistory | IComment) => {
if(entry.isHistory === true) {
entry.timeStamp //ok
} else {
entry.comment //ok
}
})
Another possibility would be to use a User-Defined Type Guard, ie a function that helps the compiler to derive whether a parameter has a certain type. 另一种可能性是使用用户定义的类型防护,即帮助编译器得出参数是否具有特定类型的函数。 The following code should solve your specific issue - i added comments to the changed bits. 以下代码应解决您的特定问题-我在已更改的位中添加了注释。
interface IComment extends IData {
comment: string;
}
interface IHistory extends IData {
differences: any[];
timeStamp: number;
}
interface IData {
user: string;
date: Moment | string;
isHistory: boolean;
}
const data: Array<IHistory | IComment> = [];
data.map((entry: IHistory | IComment) => {
// Explicitely narrows down the type to IHistory within the block
if (isHistory(entry)) {
// entry.timeStamp
} else {
// entry.comment
}
});
// User-Defined Type Guard
function isHistory(data: IData): data is IHistory {
return data.isHistory;
}
See Advanced Types at User-Defined Type Guards for more info. 有关更多信息,请参见用户定义类型防护中的 高级类型 。
You can use "in" for this case.在这种情况下,您可以使用“in”。
if('timeStamp' in entry) {
entry.timeStamp
} else {
entry.comment
}
Documentation: https://www.typescriptlang.org/docs/handbook/advanced-types.html#type-guards-and-differentiating-types文档: https : //www.typescriptlang.org/docs/handbook/advanced-types.html#type-guards-and-differentiating-types
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