title: How to update `BehaviorSubject` single value alone
body: <p>In my <code>BehaviorSubject</code> the address element having 2 property. In this how to update a single property alone?</p>
  
  <p>here is my try:</p>
  
  <pre><code>myAddress:any = {
      "plot":32,
      "street":"D15 Road"
    }
  
    private address = new BehaviorSubject(this.myAddress);
    addressClass = this.address.asObservable();
  
  
    updateAddress(newAddress){
      this.address.next(newAddress);
    }
  </code></pre>
  
  <p>I am trying to update like this:</p>
  
  <pre><code>import { Component, Input, OnInit } from '@angular/core';
  import { SharedObject } from './shared.object';
  
  @Component({
    selector: 'hello',
    template: `
      &lt;h1&gt;Hello {{name}}!&lt;/h1&gt;
      &lt;h2&gt;City Name in Hero : {{heroName}}&lt;/h2&gt;
      &lt;h3&gt;{{plotNo}}&lt;/h3&gt;
      &lt;button (click)="updatePlot(44)"&gt;Update Ploat &lt;/button&gt;
    `,
    styles: [`h1 { font-family: Lato; }`]
  })
  export class HelloComponent  {
  
    @Input() name: string;
  
    plotNo:number;
    address:any;
  
  
    constructor(private shared:SharedObject){
  
    }
  
    ngOnInit(){
       this.shared.addressClass.subscribe((address) =&gt; {
         this.plotNo = address.plot;
       })
    }
  
  
    updatePlot(newNo){
      this.shared.updateAddress(newNo); //don't know how to update plot no alone?
    }
  
  }
  </code></pre>