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

function isStrictMode() {
    try{var o={p:1,p:2};}catch(E){return true;}
    return false;
}

Looks like you already got an answer. But I already wrote some code. So here

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

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.