javascript check if not undefined

if (typeof myVar !== "undefined") {
    console.log("myVar is DEFINED");
}

if(myVar === null) {
	console.log("Element is undefined");
}

if (typeof myVariable === 'undefined'){
    //myVariable is undefined
}

let id;

if(typeof id === 'undefined') {
    console.log("id is undefined...");
}

let foo = undefined
//will return true
typeof foo === 'undefined'

if(undefinedElement === null) {
	console.log("Element is undefined");
}

javascript check number against undefined