Quiz Questions

What is `"use strict";`?

What are the advantages and disadvantages to using it?

Quiz Topics

'use strict' is a statement used to enable strict mode to entire scripts or individual functions. Strict mode is a way to opt into a restricted variant of JavaScript.


  • Makes it impossible to accidentally create global variables.
  • Makes assignments which would otherwise silently fail to throw an exception.
  • Makes attempts to delete undeletable properties throw an exception (where before the attempt would simply have no effect).
  • Requires that function parameter names be unique.
  • this is undefined in the global context.
  • It catches some common coding bloopers, throwing exceptions.
  • It disables features that are confusing or poorly thought out.


  • Many missing features that some developers might be used to.
  • No more access to function.caller and function.arguments.
  • Concatenation of scripts written in different strict modes might cause issues.

Overall, the benefits outweigh the disadvantages and there is not really a need to rely on the features that strict mode prohibits. We should all be using strict mode by default.