Is there any way to check if strict mode is enforced?

Question

Is there anyway to check if strict mode 'use strict' is enforced , and we want to execute different code for strict mode and other code for non-strict mode. Looking for function like isStrictMode();//boolean

Answer 1

The fact that this inside a function called in the global context will not point to the global object can be used to detect strict mode:

var isStrict = (function() { return !this; })(); 

Demo:

> echo '"use strict"; var isStrict = (function() { return !this; })(); console.log(isStrict);' | node true > echo 'var isStrict = (function() { return !this; })(); console.log(isStrict);' | node false 

Answer 2

I prefer something that doesn't use exceptions and works in any context, not only global one:

var mode = (eval("var __temp = null"), (typeof __temp === "undefined")) ?      "strict":      "non-strict"; 

It uses the fact the in strict mode eval doesn't introduce a new variable into the outer context.