Background

Though it is easy to replicate this functionality (eg: sinon.match(x => s instanceof foo)), the fact that this is not supported out-of-the-box can produce confusion, as the behaviour of instanceOf matchers and the instanceof operator differs regarding [Symbol.hasInstance].

Solution

This PR addresses this issue by lifting the limitation to allow not only functions, but any object with [Symbol.hasInstance] method, as defined by the standard, if supported by the interpreter.

How to verify

1. Check out this branch
2. npm install
3. node (make sure your node version supports ES6 symbols)
4. var sinon = require("./")
5. var matcher = sinon.match.instanceOf({ [Symbol.hasInstance]: () => true })
6. matcher.test("foo") // returns true

Checklist for author

• npm run lint passes
• References to standard library functions are cached.