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:

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 …

Feb 22, 2011 · NaN. See for yourself. console.log (null-undefined). The difference between null and undefined is NaN. (Note that this is an attempt at humour, before you flame me for …

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 …

Apr 22, 2009 · The biggest misconception in many of the answers here is that 'undefined' is a Javascript keyword. It's not a keyword at all, but a variable that (most of the time) happens to …

Jun 14, 2017 · The reason is that in typescript a question mark is optional. The optional is with undefined and not null. Meaning that there is a big difference between the two. Like that …

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: …

Feb 2, 2019 · Alternatively, you can type name1 as string | undefined, and handle cases of undefined further down. However, it's typically better to handle unexpected errors earlier on. …

typeof MyVariable == 'undefined' doesn't discern between an initialized variable with an undefined value and an undeclared variable unless the variable was initially declared and initialized to …

Nov 6, 2014 · undefined is a special type where it simply indicates that the variable language is not initialized or may be it's not yet defined. null in javascript simply indicates absence of a …