• VSCode Version: 1.28.0
• OS Version: Debian GNU/Linux buster/sid , Linux 4.16.0-2-amd64 1 SMP Debian 4.16.16-2 (2018-06-22) x86_64 GNU/Linux

Steps to Reproduce:

There is a Promise polyfill (class PolyfillPromise) defined in vscode/src/vs/base/common/winjs.polyfill.promise.ts. The comments say A polyfill for the native promises, but the then and catch methods do not support chaining, eg.

PolyfillPromise.resolve(1).then(function(x){return x+1}).then(function(x){console.log("Result is " + x)})

will print Result is undefined (it should print Result is 2).

Chaining is a very common operation with Promises. IE11 does not have native promises, so it uses the polyfill. This results in the ESM build of https://github.com/Microsoft/monaco-editor not working in IE11, as webpack uses Promises for dynamic imports.