null-undefined.js

/* unassigned variable */
let name;
console.log(name);
// Output: undefined

/* No return/ nothing after return */
function add(num1, num2) {
	result = num1 + num2;
	return;
}
result = add(10, 30);
console.log(result);
// Output: undefined

/* passing incorrect parameter */
function add(num1, num2) {
	console.log(num1, num2);
}
result = add();
// Output: undefined

/* passing incorrect parameter */
function add(num1, num2) {
	console.log(num1 + num2);
}
result = add();
// Output: NaN;

/* Accessing non-existing index/property */
const userData = {
	name: "Jhon Doe",
	phone: "123263",
};
console.log(userData.id);
// Output: undefined

userData.address = undefined;
console.log(userData.address);
// Output: undefined