I have rather complex code that is executing a multiple AJAX call in sequence through the \'for\' loop. This code works because I use \'Let\' statement when assigning scope
See this ES6 support table. Internet Explorer 11 does not support let
in for/for-in loop iteration scope.
You need to take a different approach.
This answer lists a number of options you could implement manually.
You could also use a tool like Babel to transpile your ES6 or newer JavaScript into ES5.