If it is undefined, it will not be equal to a string that contains the characters "undefined", as the string is not undefined. You can check the type of the variable:

Feb 22, 2011 · undefined cannot be an empty wall if the holder represents the variable. In this representation, undefined is an empty holder while null is an empty holder with post-it note empty. …

May 7, 2009 · Assigning undefined to a variable though is probably confusing, since it's a bit of a paradox (you've defined the variable as undefined) and it's not possible to distinguish that variable …

Dec 17, 2013 · There are 3 undefined in javascript. The global variable undefined, the value undefined and the type undefined. Even if the global variable undefined is overridden, the value undefined still …

Apr 22, 2009 · The object.x === undefined should return true if x is unknown property. In chapter , Crockford writes the following: If you attempt to extract a value from an object, and if the object does …

While literally using the keyword undefined, Boolean(undefined) works, trying that with an undefined variable doesn't work, and that is the whole point of doing the check for null or undefined.

Deseo determinar si una variable no está definida o si tiene el valor nulo. En el siguiente ejemplo, quiero que se ejecute la clásula correspondiente a la condición verdadera, es decir se imprima ...

Jan 18, 2011 · 391 The jQuery Core Style Guidelines suggest two different ways to check whether a variable is defined. Global Variables: typeof variable === "undefined" Local Variables: variable === …

I can't find any difference between typeof somevar == 'undefined' and typeof somevar === 'undefined', because typeof always returns string. For null it will return 'object'. Or could be that I am wrong?

Dec 31, 2009 · 1 In JavaScript, the following values will cause the if condition to fail and not execute its statement: null, undefined, false, NaN, the number 0, and the empty string ''. Assuming that the …