Paypal api – How to get global variable to stay in angular constructor & promise, calling a func that needs the data from dif component

Not an expert at angular far from it. But I’ve been looking deeply and i cant figure out why my other components that call the function types, runs before the constructor. and to solve it where do i put the " echo " function? everything works likes a charm except for the fact that echo is called before types. what or how do i make echo come first to run before any other function. i cant hook it up to the promise because it takes data from another component. i ran a if statement to check if the global variable exist and obviously doesn’t because of the order of processes.

import { Injectable, OnInit, OnDestroy } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http'
import { Observable, of } from "rxjs";
import { Router, ActivatedRoute } from '@angular/router';
import { Location } from '@angular/common/'
import { DataService } from './products.service';
import { BehaviorSubject, Subscription } from 'rxjs';
import { map } from 'rxjs/operators';
@Injectable({ providedIn: "root" })
export class CartService implements OnInit, OnDestroy {
  public data: any = { "productObjs": [] }
  public array: any;
  public datap: any;
  private sub: Subscription;
  //loop up the id if specexist remove thespec if empty remove id
  constructor(public dataservice: DataService, private http: HttpClient) {
    this.echo()
  }
  echo() {
    let headers = new HttpHeaders();
    headers.append('Content-Type', 'application/json');
    let prom = new Promise((resolve, reject) => {
      this.http.get('../assets/productCategories/products.json', { headers }).toPromise().then((data: any) => {
        console.log(data)
        var dat = this.datap
        resolve(dat)
        this.datap = data
        return dat
      }).then((dat) => { this.nextt(dat) });
    })
    return this.datap;
  }
  nextt(datap) {
    console.log(datap)
    this.datap = datap
  }
// types is called from another component and runs before promise finishes
  types(type) {
    if (this.datap) {
      console.log(this.datap)
      let that = this
      var func = type.func
      var rtype = type.type
      var arr;
      switch (func) {
        case "random":
          return that.sortByRandom()
          break;
        case "category":
          return that.sortByCategory(rtype)
          break;
        default: "specific"
          return that.sortBySpecific(rtype)
      }
      console.log(this.array)
      console.log(this.array)
      console.log(this.array)
      console.log(this.datap)
      return this.array;
    }
  }
  getArray() {
    if (this.datap) {
      console.log(this.array)
      return this.array
    }
  }
  sortBySpecific(specific) {
    let that = this
    console.log(that.datap)
    var type = that.datap.product.filter(function(objj) {
      return objj.type === specific;
    })
    return type
  }
  sortByCategory(category) {
    let that = this
    var type = this.datap.product.filter(function(objj) {
      return objj.productCategory === category;
    })
    return type
  }
  sortByRandom() {
    var cats = []
    var picked = []
    var sproducts;
    let that = this
    this.datap.productObjs.forEach((obj) => {
      var randomnum2 = Math.floor(Math.random() * this.datap.productObjs.length)
      cats.push(obj.category)
    })
    var randomnum = Math.floor(Math.random() * cats.length)
    var selectedCats = this.datap.product.filter(function(objj) {
      return objj.productCategory === cats[randomnum];
    });
    sproducts = selectedCats
    var x = sproducts[Math.floor(Math.random() * sproducts.length)]
    picked.push(x)
    that.array = picked
    return picked
  }
  addToCart(ps, pobj) {
    var checkarray = this.data.productObjs.filter(function(obj) {
      return obj.productSpec === ps;
    });
    console.log(checkarray)
    if (checkarray.length <= 0) {
      this.data.productObjs.push(pobj)
    }
  }
  getItems() {
    return this.data.productObjs
  }
  clearCart() {
    this.data.productObjs = []
  }
  clearProduct(objspec) {
    var newarray = this.data.productObjs.filter(function(obj) {
      return obj.productSpec !== objspec;
    });
    this.data.productObjs = newarray;
  }
  changeInventory() {
    //update pricing from inputs
  }
  checkout() {
    this.http.post('http://localhost:4201/api', this.data).subscribe((res) => {
      console.log(res)
      var json = res
      if (json['bool'] === "false") {
        //cant check out
        // this checks inventory also.
        //pop up error problem with pricing.
      }
      if (json['bool'] === "true") {
        //can check out
        //neeeds to request paypal to send productinfo and once payment response is succeded send valid, and delete from database.
      }
    })
  }
  ngOnInit() {
  }
  ngOnDestroy() {
    this.sub.unsubscribe();
    console.log(this.sub)
    console.log(this.datap)
  }
}