In JavaScript, the typeof operator returns the data type of its operand in the form of a string. The operand can be any object, function, or variable.
console.log(typeof undeclaredVariable); // "undefined"
let a;
console.log(typeof a); // "undefined"
const b = "Hello World";
console.log(typeof b); // "string"
const c = 42;
console.log(typeof c); // "number"
const d = 3.1415;
console.log(typeof d); // "number"
const e = true;
console.log(typeof e); // "boolean"
const f = null;
console.log(typeof f); // "object"
const g = undefined;
console.log(typeof g); // "undefined"
const h = { b: "c" };
console.log(typeof h); // "object"
const i = function () {
return 10;
};
console.log(typeof i); // "function"