Js file type inference error

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common "Bugs" That Aren't Bugs section! Please help us by doing the following steps before logging an issue: * Search: https://github.com/Microsoft/TypeScript/search?type=Issues * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ Please fill in the *entire* template below. --> <!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.2.2 **Code** **person.js** ```javascript let student = function () { this.age=12; } let person = {}; person.name=22; student.prototype=person; let tom = new student(); exports.tom =tom; ``` **test.ts** ```javascript import * as person from './person'; person.tom.name ``` **Expected behavior:** `person.tom.name` is not an error **Actual behavior:**