Rewrite BehaviorSuject that takes either localStorage or Observable in Angular
I think the ngOnInit() is the best suitable way for that. Clean and easy to spot. The initialization of the other two variables should also be part of ngOnInit (employee and employeeToken).
Something like that:
employee: Empoyee;
employeeToken: Observable&lt;string&gt;;
currentHead: BehaviorSubject&lt;ADD-TYPE-HERE&gt;;

...

ngOnInit() {
    const headFromStorage = localStorage.getItem('head');
    employee = this.identityService.me;
    employeeToken = this.employee.pipe(map((e) =&gt; e.token));
    this.currentHead = new BehaviorSubject(localStorage.getItem('head'));
    
    this.employeeToken.subscribe(e =&gt; this.currentHead.next(e));
}


Not sure you need this:
if (!this.currentHead.value || this.currentHead.value === '') {

Because this is a subscription. Every time the empoloyeeToken change, you have to update it, right?