# 03. Constructor Property

All types in JavaScript (except the `null` and `undefined` values) have a `constructor` property, which is a part of the inheritance. The `constructor` property in a prototype is automatically setup to reference the constructor function. Because properties are inherited from the prototype, the `constructor` is available on the instance object too.

For example:

```javascript
const num = 150;
num.constructor === Number; // => true

const str = "abc";
str.constructor === String; // => true

const obj = {};
str.constructor === Object; // => true

const reg = /\d/g;
reg.constructor === RegExp; // => true
```

It serves as a public identity of the class, which means it can be used for:

* Identify to what class belongs an object (an alternative to `instanceof`)
* Reference from an object or a prototype the constructor function
* Get the class name

## Constructors for primitive types

In JavaScript the primitive types has a constructor property, which refers to the corresponding type function:

* `Number()` for numbers: `(1).constructor === Number`
* `Boolean()` for boolean: `(true).constructor === Boolean`
* `String()` for strings: `('hello').constructor === String`
* `Symbol()` for symbols: `Symbol().constructor === Symbol`

`constructor` is a regular non-enumerable property in the prototype object. It does not update automatically when a new object is created based on it. When creating a subclass, the correct constructor should be setup manually.