JSFiddle - React, Tailwind, and code Playground

JavaScript

"use strict";
let x = 15;
alert(x);
// language:javascript
// IE11, Chrome41 - works fine
// Firefox36 - error "let is a reserved identifier"
// Safari8 - error "unexpected use of reserved word let"

// language:javascript1.7
// IE11, Chrome41 - not recognized as JS
// Firefox36 - works fine
// Safari8 - error "unexpected use of reserved word let"