Using Primitive Wrapper Object to Wrap Number | 點燈坊

In addition to using Primitive for Number, we can use Primitive Wrapper Object to wrap Number.

Version

ECMAScript 2015

typeof

let x = 1
let y = new Number (1) // ?

typeof x // ?
typeof y // ?

• x is Number Literal
• y is a Wrapper Object for Number
• typeof :
  • Number Literal : number
  • Wrapper Object : object

instanceOf

let x = 1
let y = new Number (1) // ?


x instanceof Number // ?
y instanceof Number // ?

instanceof :

• Number Literal : false
• Wrapper Object : true

valueOf

let x = 1
let y = new Number (1) // ?

x === y.valueOf () // ?

We can use valueOf to unwrap Wrapper Object.

Number

let x = 1
let y = new Number (1) // ?

x === Number (y) // ?

We can also use Number to unwrap Wrapper Object.

Dynamic Property

let x = 1
let y = new Number (1) // ?

y.id = 2

y // ?
y.id // ?

Since Wrapper Object is an Object, we can add a new property to Primitive Wrapper Object.

Conclusion

• Primitive Wrapper Object is immutable. We can’t modify the inner value of Wrapper Object

Reference

MDN, Number