javascript check for undefined

if (typeof myVariable === 'undefined'){
    //myVariable is undefined
}if (typeof myVar !== "undefined") {
    console.log("myVar is DEFINED");
}//detecting undefined object property
if (typeof person.last_name === "undefined") {
    console.log("person last_name is undefined");
}

//detecting undefined variable 
if (typeof myVar === "undefined") {
    console.log("myVar is undefined");
}