联合中不存在 Typescript 属性 [英] Typescript property does not exist in a union

问题描述

我有以下类型:

Foo {
 foobar: any
}

Bar {
 fooBarBar: any;
}

定义如下的函数:

this.api.submit(param: Foo | Bar)

用法:

this.api.submit(param.foobar) // does not exist on Bar

Error: Property 'foobar' does not exist on type 'Foo| Bar'.
  Property 'foobar' does not exist on type 'Bar '

我的假设是 typescript 会根据联合计算它可能是这些模型中的任何一个，那么为什么它会在这种情况下抱怨?

My assumption was typescript would figure based on the union it could be either of these models, so why does it complain in this instance?

一种解决方法是使用括号表示法 param['foobar'] 并且错误将消失...

A workaround is to use the bracket notation param['foobar'] and the error will disappear...

推荐答案

你的定义是说 param 将是 either Foo 或Bar，但编译器无法决定在您调用 param.foobar 时调用哪个.

What your definition says is that param will be either Foo or Bar, but there's no way for the compiler to decide which at the point you call param.foobar.

如果你想能够区分，你可以这样做:

If you want to be able to discriminate, you can do something like this:

Foo {
    type: 'foo',
    foobar: any
}

Bar {
    type: 'bar',
    fooBarBar: any;
}
...
if (param.type === 'foo') {
    param.foobar; // the type guard in the if statement guarantees we've got an instance of Foo here
}

如果你想说 param 将是 both Foo 和 Bar，你需要 交叉点类型，即:Foo &条形.

If what you wanted to say is that param will be both Foo and Bar, you need intersection types, i.e.: Foo & Bar.

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