How to support promises in Internet Explorer 11?

I have a simple code that runs perfectly on every browser except for the Internet Explorer 11. How can I make it work on all browsers?

Codepen

'use strict';

let promise = new Promise((resolve, reject) => {

  setTimeout(() => {
    resolve("result");
  }, 1000);
});

promise
  .then(
    result => {
      alert("Fulfilled: " + result);
    },
    error => {
      alert("Rejected: " + error);
    }
  );