调用 spyOn(service，'a')后， service.a 不再是您在函数中定义的 a -这是一个间谍函数.该间谍函数恰巧调用了 a ，但它不是 a ；它具有不同的身份，并且具有不同的功能.

After you call spyOn(service, 'a'), service.a is no longer the a you defined in the function -- it is a spy function. That spy function happens to call a, but it is not a; it has a different identity and is a different function.

但是，设置 service 的 a 属性不会更改您在 app.factory 中声明的 function a >.您只需更改 service ，以使其 a 属性不再引用原始的 a .相比之下，您的 b 函数永远不会将其引用更改为原始的 a .它直接从最初声明了 a 和 b 的本地 app.factory 范围获取 a . service 用间谍替换其原始 a 的事实不会影响 b 对 a()的调用，因为它没有引用 service.a .

However, setting the a property of service does not change the function a you declared inside app.factory. You've simply changed service so that its a property no longer refers to your original a. By contrast, your b function never changes its reference to the original a. It gets a straight from the local app.factory scope in which a and b were originally declared. The fact that service replaces its original a with a spy does not affect b's call to a(), because it does not refer to service.a.