use strict Directive
use strict is placed either between single quotes (
'') or double quotes (
""). There are no keywords in this statement. Future versions of the ECMAScript standard are expected to introduce
use as a new keyword. If this happens, there will no longer be a need for quotation marks.
"use strict" directive can appear either at the beginning of your script or at the beginning of a function's body. Any string literal expression statements that come after the first regular statement in a script or function will be interpreted as an ordinary expression statement and will have no side effects. These statements will not be interpreted as directives.