ERROR - This language feature is only supported for ECMASCRIPT6 mode or better: let declaration.

ECMAScript 2015 was the second major revision to JavaScript. ECMAScript 2015 is also known as ES6 and ECMAScript 6.

Issue:

ERROR - This language feature is only supported for ECMASCRIPT6 mode or better: let declaration.
 

Workaround:

The let keyword is not supported to declare a variable. Instead of let try using the var.