Why is the output 0 here. var a = 7; a.constructor();

Question

Let's look at the examples below:

Q1: Why is the output 0 here? What does it mean?

var a = 7;
console.log(a.constructor()); // prints 0 (Why?)

Q2: When typeof a and typeof 7 both are number, why a.constructor() runs whereas 7.constructor() doesn't?

var a = 7; 
var bool = typeof a === typeof 7;

console.log(a.constructor()); // 0
console.log((++a).constructor()); // 0

console.log(7.constructor()); // SyntaxError: Invalid or unexpected token
console.log(++a.constructor()); // ReferenceError: Invalid left-hand side expression in prefix operation

Answer 1

Q1: Why is the output 0 here? What does it mean?

a.constructor is Number and you are calling it with first argument undefined. Because Number() returns undefined so x.constructor() returns undefined. If no argument is passed to Number() it returns 0

var a = 5;
console.log(a.constructor === Number)
console.log(Number())

When typeof a and typeof 7 both are number, why a.constructor() runs whereas 7.constructor() doesn't?

Actually 7. is itself a number. Here . doesnot work as Dot Notation but as decimal point because the digits after decimal point are optional.

Solution:

There can be different ways to directly access the method of number.

console.log(5..constructor)
console.log((5).constructor)
console.log(5 .constructor)