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I am new to Angular and recently start to learn it by reading a book 'ng-book The Complete Book on Angular 4'. In the 'how angular works' chapter I wrote a small inventory app followed by the instructions on the book but having issue after startup, shown as below: error log on browser console
All my components seem alright and the errors are just not seem relevant to my code. I even compared to the example code downloaded and they look very identical.
I know it's probably not that much of a big deal and I should move on and go back to this when I gain more knowledge. But really it's bothering me...
Not sure what's the best way of showing all my source code here so I created a shareable google drive link and a .zip with everything in that project can be retrieved by the link. ANY HELP WILL BE HIGHLY APPRECIATED!!!
https://drive.google.com/file/d/0B76fFkACV6wRdmtJU0Jfc0J4U1U/view?usp=sharing
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To solve the "Cannot read properties of undefined" error, make sure that the DOM element you are accessing exists. The error is often thrown when trying to access a property at a non-existent index after using the getElementsByClassName() method. Copied!
This issue means that something has been replaced with a mock object and returns a dummy result ( undefined ) instead of observable streams. There is an answer for this error in the section called How to mock observables, if the error has been triggered by a mock service, and its property is of type of undefined .
Subscribe() is a method in Angular that connects the observer to observable events. Whenever any change is made in these observable, a code is executed and observes the results or changes using the subscribe method. Subscribe() is a method from the rxjs library, used internally by Angular.
In ProductsListComponent, you need to change :
@Output() onProductSelected: EventEmitter<Product>;
to :
@Output() onProductSelected = new EventEmitter<Product>();
Also, remove the line in ngOnInit in the same component.
The event emitter needs to be initialized when the class is created. See this example : http://learnangular2.com/outputs/
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