Explanation of the difference between determining whether a function is new or called in JavaScript

Method 1

Copy the codeThe code is as follows:

 
function Person(n,a){ 
 = n; 
 = a; 
if(this instanceof Person){ 
alert('new call');
}else{ 
alert('function call');
} 
} 
var p = new Person('jack',30); // --> new call
Person(); // --> Function Call

Method 2

Copy the codeThe code is as follows:

 
function Person(n,a){ 
 = n; 
 = a; 
if(this instanceof ){ 
alert('new call');
}else{ 
alert('function call');
} 
} 
var p = new Person('jack',30); // --> new call
Person(); // --> Function Call

Method 3

Copy the codeThe code is as follows:

 
function Person(n,a){ 
 = n; 
 = a; 
if( === ){ 
alert('new call');
}else{ 
alert('function call');
} 
} 
var p = new Person('jack',30); // --> new call
Person(); // --> Function Call

It seems perfect, but when calling a function/class as a method of its own instance object, it will be a problem

Copy the codeThe code is as follows:

 
function Person(n,a){ 
 = n; 
 = a; 
if( === ){ 
alert('new call');
}else{ 
alert('function call');
} 
} 
var p = new Person('jack',30); // New object first
= Person; // Assign function/class Person to the fn attribute of its own object p
(); // This sentence prompts "This is a new call", which is obviously wrong

Is there a better way?