In the Google style guide for written JavaScript ( prove the link ) that using the "const" construct is bad practice, why?
Because it is not standard (yet). This is a JavaScript 1.5 keyword, not ECMAScript. From the MDN documentation:
const Mozilla ECMAScript 5. Firefox Chrome (V8) Opera 9+ Safari. Internet Explorer 6-9 Internet Explorer 10. const (, , var).
const
, , , :
const, Internet Explorer , .