@observe.async

The @async decorator sets up the value to be connected to the result of an asynchronous call, such as an API request or a promise.

When attached to a method, it passes a resolve argument, which you call to set the value. When attached to a getter, it expects the return value to be a promise (specifically, a thenable) or undefined (for no changes);

import observe from "can-observe";

class Thing extends observe.Object {
    @observe.async
    fullName( resolve ) {
        setTimeout( function() {
            resolve( this.first + " " + this.last );
        }.bind( this ), 0 );
    }

    @observe.async
    get formalName() {
        return new Promise( ( resolve ) => {
            setTimeout( function() {
                resolve( this.last + ", " + this.first );
            }.bind( this ), 0 );
        } );
    }
}