JavaScript check if variable exists (is defined/initialized)

Question

Which method of checking if a variable has been initialized is better/correct? (Assuming the variable could hold anything (string, int, object, function, etc.))

Answer 1

Try-catch

If variable was not defined at all, you can check this without break code execution using try-catch block as follows (you don't need to use strict mode)

try{
  notDefinedVariable;
} catch(e) {
  console.log('detected: variable not exists');
}

console.log('but the code is still executed');

notDefinedVariable; // without try-catch wrapper code stops here

console.log('code execution stops. You will NOT see this message on console');

BONUS: (referring to other answers) Why === is more clear than == (source)

if( a == b )

if( a === b )