The instanceof Operator

The instanceof operator returns true if an object is an instance of a specified type.

// Create a Date
const time = new Date();

(time instanceof Date);

// Create an Array
const fruits = [“apples”, “bananas”, “oranges”];

(fruits instanceof Array);

// Create a Map
const fruits = new Map([
[“apples”, 500],
[“bananas”, 300],
[“oranges”, 200]
]);

(fruits instanceof Map);

// Create a Set
const fruits = new Set([“apples”, “bananas”, “oranges”]);

(fruits instanceof Set);

Undefined Variables

The typeof an undefined variable is “undefined.”

typeof car;

The typeof a variable that has no value is “undefined,” and its value is also undefined.

let car;
typeof car;

Any variable can be cleared by setting its value to undefined, which will also make its type undefined.

let car = “Volvo”;
car = undefined;