auth-interceptor.ts

import { HttpRequest, HttpHandler, HttpEvent, HttpInterceptor } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';

@Injectable()
export class JWTInterceptor implements HttpInterceptor {

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        if (req.method === 'DELETE' || req.method === 'POST' || req.method === 'PUT') {
            let currentUser = JSON.parse(localStorage.getItem('currentUser'));
            if (currentUser && currentUser.token) {
                req = req.clone({
                    setHeaders: {
                        authorization: 'Bearer ' + currentUser.token
                    }
                });
            }
        }
        return next.handle(req);
    }
}