JS: Primitive Value

By Xah Lee. Date: . Last updated: .

Primitive Value

A primitive value is a value whose Type is a primitive type.

Primitive Value Object Wrapper

many primitive types have a corresponding object wrapper class.

“Autoboxing” object wrapper on primitives

Some primitive values have object wrapper, so that you can call methods on them.

For example, when you want to know the length of string, you do 

console.log("abc".length);

.length is a property access, and property is available only for object.

what happens is that JavaScript has objects for many primitive types, so that lets you to have methods on primitives, such as string and nunmbers.

when you call a method on a primitive, JavaScript temporarily converts the primitive to a corresponding object, calls the method, then convert it back to primitive value.

Convert Primitive Value to Object

You can create object version of the primitives yourself.

or use the constructors: 

const aa = Object("abc");
const bb = new String("abc");

console.log(aa);
// [String: "abc"]

console.log(bb);
// [String: "abc"]

console.log(typeof aa === "object");
// true
console.log(typeof bb === "object");
// true
console.log(String(aa) === String(bb));
// true

JavaScript. Value Types