Can you / how do you add a constructor into an object?

Question

Is it possible to add a constructor to an object?

If the following were possible, I would like to accomplish something like:

const constructorObject = {
  Constructor: Constructor("content")
}

If this object were accessed you would be able to do the following:

new constructorObject.constructor({ content: "content" }):

without getting an error saying:

undefined is not a constructor 
(evaluating 'new constructorObject.Constructor({ content: "content })')

For context, I have a react component, and I'm making a call to the googleAPI in a parent component.

this.googleAPI is passed to the child . When I'm running the test - props are passed to the child but without a constructor in the object - the test fails.

In the childComponent the init is called on mount :

init() {
   const { position, map, title, icon } = this.props;
   this.marker = new this.props.googleApi.Marker({
     icon,
     position,
     map,
     title
   });
}

In the Enzyme test:

import React from "react";
import { shallow } from "enzyme";
import Child from "src/components/child";

describe("components/child", () => {
  let props;
  beforeEach(() => {
    props = {
      googleApi: {},
      map: {},
      position: {
        lat: 10,
        lng: 10
      },
      title: "title",
      icon: "icon"
    };
  });

  describe("on mount", () => {
    it("should render into the document", () => {
      const component = shallow(<Marker {...props} />);
      expect(component).to.not.be.null;
    });
  });
});

This is the enzyme error:

undefined is not a constructor (evaluating 'new this.props.googleApi.Marker({ title: this.props.title })')

Answer 1

One would usually mock the external resources using something like jest . in this case i would assume that would be googleAPI .

When initializing props in beforeEach ,

if you want to add an addListener that is a constructor within your Marker I would try :

let props;
let component;
beforeEach(() => {
    props = {
      googleApi: {
        Marker: () => ({ addListener: jest.fn() })
      },
    };
    component = shallow(<Marker {...props} />);
});

If you just need a function you can do:

props = {
      googleApi: {
        ChildComponent: () => ({ click: jest.fn() }),
        event: {
          addListener: jest.fn()
        }
      }
    }

https://jestjs.io/docs/en/mock-functions for more info.

Answer 2

In JS a constructor can be just a function. See this . Basically this should work for you:

beforeEach(() => {
  props = {
    googleApi: {
      Marker: () => {}
    },
    map: {},
    position: {
      lat: 10,
      lng: 10
    },
    title: "title",
    icon: "icon"
  };
});