Typescript对象的属性 [英] Typescript casting object's property

问题描述

我使用indexeddb和typescript。我的问题是TS似乎不能处理 event.target.result 属性。例子：

I'm working with indexeddb and typescript. My issue is that TS doesn't seem to be able handle the event.target.result property. Case in point:

request.onsuccess = (event) => {
    namespace.db = event.target.result; //the property 'results' does not 
                                        //exist on the value of type 'EventTarget'
    var a = event.target;
    var b = <IDBOpenDBRequest>a;
    var c = b.result; // <-- magically there's a results property here

    version = parseInt(namespace.db.version);
    console.log("version: " + version);
    deferred.resolve();
}

所以我的问题是：有更简单的方法来投入目标属性到< IDBOpenDBRequest> 其他然后 a c $ c> b

So my question is: Is there an easier way to cast the target property to <IDBOpenDBRequest> other then the a, b method above?

推荐答案

如果你正在寻找一个oneliner它通过添加一些额外的括号，如此：

If you are looking for a oneliner you can cast it by adding some extra parenthesis like so:

indexedDB.open("test", 1).onsuccess = (ev) => {
    var result: IDBDatabase = (<IDBOpenDBRequest>ev.target).result;
}

也请注意：IDBDatabase ，因为结果在Typescript定义文件中被定义为 any 。它不是必需的，但使用它作为一个任何类型将意味着没有类型检查由编译器。

Also notice the : IDBDatabase because result is typed as any in the Typescript definition file. It isn't needed but using it as an "any" type would mean no typechecking by the compiler.

现在你可以使用的结果，如下所示： http://www.w3.org/TR/IndexedDB/#database-interface

Now you can use the result like you want with the methods available as defined here: http://www.w3.org/TR/IndexedDB/#database-interface

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