Is it possible to create a new data type in JavaScript?

Question

Is it possible to create a new data type in JavaScript, like string?

Example: I have the variable person and I want to declare that the type of that variable is Person.

Like this:

var person = "idk" console.log(typeof person)  

Output: "Person"

Answer 1

The closest you can get to what you're describing is testing instanceof, or using instanceof to create your own type checking function:

class Person {   constructor(name, age) {     this.name = name;      this.age = age;   } }  const bill = new Person("Bill", 40);  function checkType(data){   if(data instanceof Person) return "Person";   return typeof data;  }  console.log(bill instanceof Person); console.log(checkType(bill)); console.log(checkType("bill"));