Specify a property's get behavior with the get syntax.

import { ObservableObject } from "can/everything";

class Example extends ObservableObject {
  get propertyName() {
    return true;
  }
}

const e = new Example();
console.log( e.propertyName ); //-> true

For example:

import { ObservableObject } from "can/everything";

class Person extends ObservableObject {
  static props = {
    first: String,
    last: String
  };

  get fullName() {
    return this.first + " " + this.last;
  }
}

const person = new Person( {first: "Justin", last: "Meyer"} );
console.log( person.fullName ); //-> "Justin Meyer"

This is a shorthand for providing an object with a get property like:

import { ObservableObject } from "can/everything";

class Person extends ObservableObject {
  static props = {
    first: String,
    last: String,
    fullName: {
      get() {
        return this.first + " " + this.last;
      }
    }
  }
}

const person = new Person( {first: "Justin", last: "Meyer"} );
console.log( person.fullName ); //-> "Justin Meyer"

You must use an object with a get property if you want your get to take the lastSetValue or resolve arguments.