BehaviorSubject gives error for next function when i try to add the variable using next().“ I get the error this.count.next is not a function”

问题

Inside Angular service i have a variable count, which i want to observe whenever it's updated, i want to set that updated value to another variable in a different component.

import {BehaviorSubject} from "rxjs/BehaviorSubject";
import 'rxjs/Rx';

export class DashboardService{
  count = new BehaviorSubject<number>(0);
  count$=this.count.asObservable();

  addCount(data){
    this.count.next(data);
  }
}

I get the error eventhough i have imported all the relevant libraries .Any idea why i'm getting this? can anyone tell me what's happening with the code ?

} rxJs version 5.4.3 latest!

回答1:

Try this:

export class DashboardService {
    count = new BehaviorSubject<number>(0);
    count$ = this.count.asObservable();

    public addCount = (data) => {
      this.count.next(data);
    }
}

The issue you are encountering is that you are using addCount in a context where this inside the function is altered (i.e. pointing to something else). Using lamda based functions in typescript ensures this can not happen. This is not an excuse for always using them however.

I recommend you read up a bit on lambda/arrow functions, it might also be a good idea to look in to how this works in javascript and in typescript.

来源：https://stackoverflow.com/questions/46452347/behaviorsubject-gives-error-for-next-function-when-i-try-to-add-the-variable-usi