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Object.defineProperty(window, 'undefinable', {get: function(){}});
//]]></script><script>//<![CDATA[

/*fail*/ function undefinable() {} // or window.undefinable = function(){};
console.log(typeof undefinable);


//]]></script><script>//<![CDATA[

/*fail*/ 'use strict'; function undefinable(){}
console.log(typeof undefinable);