– Daniel Schaffer Aug 2, 2010 at 18:09 3 See: How to check for undefined in javascript?, and whether a variable is undefined and How to handle ‘undefined’ in javascript – Shog9 Aug 3, …

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 …

May 7, 2009 · Yes, variables can have a value of undefined and you can explicitly assign values to them. Assigning undefined to a variable though is probably confusing, since it's a bit of a …

Feb 22, 2011 · As typeof returns undefined, undefined is a type where as null is an initializer indicates the variable points to no object (virtually everything in Javascript is an object).

Dec 31, 2009 · typeof foo !== 'undefined' window.foo !== undefined 'foo' in window The first two should be equivalent (as long as foo isn't shadowed by a local variable), whereas the last one …

Feb 24, 2011 · How do I check a variable if it's null or undefined and what is the difference between the null and undefined? What is the difference between == and === (it's hard to …

Aug 29, 2011 · undefined is a variable, not a constant, and can be assigned a value. Because of this, one school of thought says the second path is safer, since you cannot be sure of the …

Jan 18, 2011 · 390 The jQuery Core Style Guidelines suggest two different ways to check whether a variable is defined. Global Variables: typeof variable === "undefined" Local Variables: …

Aug 26, 2008 · How do I check if an object property in JavaScript is undefined?

If you simply do var v;, it will automatically have an initial value of undefined, so if v gets some other non-falsey value, x will be assigned that value. But if v isn't assigned anything, or gets …