Getting data asynchronously?

Question

Angular

The service has a variable: private layers = [];
Which is filled statically in the service constructor:

constructor() {
    this.layers.push({id: 1});
}

Also in the service there is an asynchronous method:

public load() {
    return this.http.load();
}

How to add the result of an async function to this.layers.push()?

The problem is that in the component where I use the service - I want to get completely filled this.layers.from the service from asynchronous filling and synchronous.

Simple example:

let a = [];

a.push(1);

setTimeout(() => a.push(4), 5000);

console.log(a);

// В компоненте получить полный a[1, 4]