What is strict mode, and why does it exist? It was created as a cleaner mode of JavaScript, catching certain kinds of coding mistakes (like typos in variable names), steering developers away from some error-prone parts of the language, and disabling some language features that are just plain bad.
Strict mode provides a number of benefits. It:
-
enforces the use of the
varkeyword -
does not require
withstatements -
places restrictions on the way the
evalfunction can be used -
treats duplicate names in a function’s parameters as a syntax error
All this just for adding the
'use strict' directive to the top of a function.
As a bonus, the 'use strict' directive is ignored by
older browsers that do not support it. (These browsers simply see the directive
as a string.)
You can read more about strict mode on the MDN at developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode.