typeof
is safer as it allows the identifier to never have been declared before:
if(typeof neverDeclared === "undefined") // no errors
if(neverDeclared === null) // throws ReferenceError: neverDeclared is not defined
typeof
is safer as it allows the identifier to never have been declared before:
if(typeof neverDeclared === "undefined") // no errors
if(neverDeclared === null) // throws ReferenceError: neverDeclared is not defined