import { filter, map } from 'rxjs/operators'
import { Component, OnInit } from '@angular/core'
import { NavigationEnd, Router } from '@angular/router'
import { getParameterByName } from '../shared/misc/utils'

@Component({
  selector: 'my-header',
  templateUrl: './header.component.html',
  styleUrls: [ './header.component.scss' ]
})

export class HeaderComponent implements OnInit {
  searchValue = ''

  constructor (private router: Router) {}

  ngOnInit () {
    this.router.events
        .pipe(
          filter(e => e instanceof NavigationEnd),
          map(() => getParameterByName('search', window.location.href))
        )
        .subscribe(searchQuery => this.searchValue = searchQuery || '')
  }

  doSearch () {
    this.router.navigate([ '/videos', 'search' ], {
      queryParams: { search: this.searchValue }
    })
  }
}

import { filter, map } from 'rxjs/operators'
import { Component, OnInit } from '@angular/core'
import { NavigationEnd, Router } from '@angular/router'
import { getParameterByName } from '../shared/misc/utils'

@Component({
  selector: 'my-header',
  templateUrl: './header.component.html',
  styleUrls: [ './header.component.scss' ]
})

export class HeaderComponent implements OnInit {
  searchValue = ''

  constructor (private router: Router) {}

  ngOnInit () {
    this.router.events
        .pipe(
          filter(e => e instanceof NavigationEnd),
          map(() => getParameterByName('search', window.location.href)),
          filter(searchQuery => !!searchQuery)
        )
        .subscribe(searchQuery => this.searchValue = searchQuery)
  }

  doSearch () {
    this.router.navigate([ '/videos', 'search' ], {
      queryParams: { search: this.searchValue }
    })
  }
}

--- 
+++ 
@@ -18,10 +18,9 @@
     this.router.events
         .pipe(
           filter(e => e instanceof NavigationEnd),
-          map(() => getParameterByName('search', window.location.href)),
-          filter(searchQuery => !!searchQuery)
+          map(() => getParameterByName('search', window.location.href))
         )
-        .subscribe(searchQuery => this.searchValue = searchQuery)
+        .subscribe(searchQuery => this.searchValue = searchQuery || '')
   }
 
   doSearch () {
Reset search on page change
