我不理解Flux中Dispatcher.js中的某些语法

Question

While reading code on Flux, I found some lines I don't understand.

Source: https://github.com/facebook/flux/blob/master/src/Dispatcher.js

1. On line 109, the angle brackets

    class Dispatcher<TPayload> 

2. On line 110-115, the whole block doesn't look like javascript.

    _callbacks: {[key: DispatchToken]: (payload: TPayload) => void}; _isDispatching: boolean; _isHandled: {[key: DispatchToken]: boolean}; _isPending: {[key: DispatchToken]: boolean}; _lastID: number; _pendingPayload: TPayload; 

3. On line 138, the function with : void before curly braces.

    unregister(id: DispatchToken): void { ...} 

I thing it is because of some kind of js library. But I'm not sure. The only trace I can find is that invariant is required for this js file. but I can't find the code or documents of invariant.

Answer 1

It isn't just Javascript (check out this line ), it's flow .

Flow adds static type checking to Javascript code.

Specifically:

1. http://flowtype.org/docs/classes.html#polymorphic-classes
2. It's a mix of es6 and Flow syntax
3. http://flowtype.org/docs/functions.html#type-annotating-functions