Typescript 3.5.1 "incompatible types" error in old code?

Question

I've some old code like this

import * as $ from "jquery";
type Foo = string | object | JQuery;

let x: Foo = { bar: 33}; // just a generic object
let y: Foo = { stop: 33}; // meant to a generic object, but...

With Typescript 3.5.1 I get this error for y.

Types of property stop are incompatible. Type number is not assignable to type { (queue: string, clearQueue?: boolean, jumpToEnd?: boolean): JQuery<HTMLElement>; (clearQueue?: boolean, jumpToEnd?: boolean): JQuery<HTMLElement>; }.

Obviously it's inferring (incorrectly) that {stop:33} is meant to be a JQuery?

Is this a compiler bug? If not, how to avoid the problem?

To explain why Foo is defined that way... It's used as a parameter type to functions, allowing the conversion of Foo to an XML string, like this. Depending on the type of Foo it's treated as an existing XML string, a DOM node, or a generic object which is translated to xml.

private paramToString(data: Foo): string {
  let result = isJquery(data) ? new XMLSerializer().serializeToString(data[0]) :
    (typeof data === "string" ? data : new XML2JS.Builder().buildObject(data));
  return result;
  }

If it's meant to be a generic object, why declare it with type Foo? I'm having trouble seeing what Foo is for. I get string | JQuery, but object? — T.J. Crowder
– T.J. Crowder, Commented Jun 7, 2019 at 7:00
Change the key name instead of stop and try. Because may be some stop() functions are there with the same name in inside of JQuery object. — Ramesh Rajendran
– Ramesh Rajendran, Commented Jun 7, 2019 at 7:02
@T.J.Crowder see my edit. Ramesh: Yes, that's what's happening, but changing the key name isn't an option for me here. — Roddy
– Roddy, Commented Jun 7, 2019 at 7:19

sl4vr · Accepted Answer · 2019-06-07 07:41:33Z

2

Yup, looks like JQuery type has stop defined and it's not a number. The simplest solution is to explicitly tell that your value is a simple object.

let y: Foo = {stop: 33} as object;

answered Jun 7, 2019 at 7:41

sl4vr

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