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javascriptreactjsdispatcherflux

I don't understand some syntax in Dispatcher.js in Flux

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.

Solution

  • 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