console.log(typeof undefined); // undefined
console.log(typeof null); // object
console.log(typeof {}); // object
console.log(typeof true); // boolean
console.log(typeof 1); // number
console.log(typeof ""); // string
console.log(typeof Symbol()); // symbol
console.log(typeof function(){}); // function
console.log("----");
let a = (typeof undefined);
console.log(typeof a); // string
console.log(void 1);