this is some open-source polyfills to implement modern web standards in Internet Explorer. let.js polyfills for let by replacing it with var. this polyfill requires ES5 and later support, so IE10 or IE11 work fine with it but IE9 and older don't. const.js polyfills for const by replacing it with var. this polyfill requires ES5 and later support, so IE10 or IE11 work fine with it but IE9 and older don't. arrow.js polyfills for arrow functions (() => {}) by replacing them with normal functions. this polyfill requires ES5 and later support, so IE10 or IE11 work fine with it but IE9 and older don't. class.js polyfills for classes using a complex mess that acts as an ES5-based class runtime of sorts. developer eyes will go pop when they see this. requires IE10 or newer because of IE10 being the first IE to have ES5 JS. the same goes for modules.js, a polyfill for import/export. templateliterals.js polyfills for template literals. I've written it so long ago I forgot how. also an IE10-and-IE11-only polyfill. defaultparams.js polyfills for default parameters. it is undescribable. restparams.js is the default parameters polyfill converted for rest parameters. spreadop.js is the spread operator polyfill. destruct.js polyfills for destructuring. Class1.cs is an unimportant little placeholder generated by VS 2015 itself. boilerplate.cs is some COM boilerplate required for hooking IE and making the polyfills load.