Observables.md

Observables -- Various Data Sources (User Input) Events, HTTp Request, Triggered in Code...

WE ALWAYS SUBSCRIBE OBSERVABLES

             * OBSERVABLE IS AN OBJEct WE IMPORT FROM A THIRD-PARTY PACKAGE -- RxJS

             * There are Observables(it's Function) and a Observer(The CODE Written) and In the Middle the Stream(EVENTS) 

In order to follow along smoothly with the course examples, make sure you install RxJS v6 by running

             *npm install --save rxjs@6
      
      In addition, also install the rxjs-compat package:
             *npm install --save rxjs-compat 

Three Functions of Observables -- NEXT, ERROR, COMPLETION

  * USING NEXT to -- EMITTING NEW DATA
  * USING ERROR to -- HANDLE ERRORS -- when an observable throws a error it Dies.
  * USING COMPLETE to -- EMITTING NEW DATA

Common Observables

 1-- params

 2-- valueChanges

Operators -- MAGIC Feature of RxJS Library -- Helps us to Transform DATA

 * They are Called by PIPE() Method

Subject -- With subject we can call the NEXT() from the OUTSIDE i.e from not inside the subscribe function

 * #Only use Subject<>() when Communicating Across Components Using Services. 

 * Subject is PERFECT for an EventEmitter CASE/SCENARIO

 * USE -- Variable = new subject<boolean>(); && we USE NEXT() to emit the Event not 
 emit() like EventEmitter