声明环境变量（如果Typescript中不为null）

Question

I have the following line declare var Notification: any; .

It's working fine, for the most part. But on iOS I see the following exception - ReferenceError: Can't find variable: Notification . iOS doesn't seem to support Notification , is there a way to check if is it null, and if it is do not declare it. Something like this -

if (Notification)
  declare var Notification: any;

Answer 1

Declare it (compile time)

declare var Notification: any;  // <= this is for the compiler only

Test it (runtime)

if (typeof Notification !== 'undefined') {   
   //non IOS stuff
}

Answer 2

Ambient declarations such as declare var are only useful during compilation time. They are not available during execution time.

The message error you have means that Notification are not defined. Using declare var will not change that fact. You miss in your code an actual instanciation/definition of your variable Notification .