Injecting an object with a .then property which is not a promise resolves to undefined

[brahms116]

When you inject an object with a property of .then but its not a promise, it resolves to undefined. This is because when resolving it believes that its a promise when its not

Expected Behavior

This should pass...

import { expect } from "chai";
import { Container, inject, injectable } from "../../src/inversify";

describe("Issue", () => {
  it("It should not return injected value as undefined if the value contains a .then property but it is not a promise", () => {
    const container = new Container();

    interface Injected {
      myProperty: string;
      then: () => number;
    }

    @injectable()
    class ResolveMe {
      constructor(@inject("Injected") public injected: Injected) {}
    }

    container.bind("Injected").toConstantValue({
      myProperty: "myNewProperty",
      then: () => 1
    });

    const me = container.resolve(ResolveMe);
    expect(me.injected.myProperty).to.eql("myNewProperty");
  });
});

Current Behavior

injected resolves to undefined

Possible Solution

I have linked a PR for a possible approach #1571

[notaphplover]

Hey @brahms116, I had a look at your issue.

Inversify relies on the Promises/A+ standard and tries to apply their resolution algorithm when it detects a thenable.

According to the standard resolution procedure, "Injected" must be resolved to the value 1.

Consider this passing test:

import { expect } from "chai";
import { Container, inject, injectable } from "../../src/inversify";

describe("Issue 1570", () => {
  it("It should not return injected value as undefined if the value contains a .then property but it is not a promise", () => {
    const container = new Container();

    interface Injected {
      myProperty: string;
      then: () => number;
    }

    @injectable()
    class ResolveMe {
      constructor(@inject("Injected") public injected: Injected) {}
    }

    container.bind("Injected").toConstantValue({
      myProperty: "myNewProperty",
      then: () => 1,
    });

    const me = container.resolve(ResolveMe);
    expect(me.injected).to.eql(1);
  });
});

This is the expected behavior when working with thenables, we cannot rely on the Promise class because it's not the only possible expected Promise. Any class implementing the Promises/A+ spec is a valid promise as well, and I would suggest you not to rely on instance of Promise to detect a Promise for such a reason.

I'll close this issue now. If you wish to continue the discussion, feel free to reply me in this issue and I'll reopen it asap.