Unresolved function or method on very basic JS class Follow

I'm using PHPStorm 2017.2, and no matter what I do, I can't get it to recognize JS methods. I've stripped it down to the most basic example I can, and still no luck.

In the example below, PHPStorm shows "Unresolved function or method exampleInstanceMethod()" for line 8. What do I need to do to fix this?

/* eslint-disable no-console */
/**
 *
 * @constructor
 */
var TestThing = function()
{
    this.exampleInstanceMethod();
};

TestThing.prototype.exampleInstanceMethod = function()
{
    console.log('hello');
};