Js file type inference error

[HSunboy]

TypeScript Version: 3.2.2

Code

person.js

let student = function () {
    this.age=12;
}
let person = {};
person.name=22;
student.prototype=person;
let tom = new student();

exports.tom =tom;

test.ts

import * as person from './person';
person.tom.name

Expected behavior: person.tom.name is not an error

Actual behavior: