Explanation of the difference between determining whether a function is called new or () in JavaScript_javascript skills

Method 1

Copy code The code is as follows:

function Person(n,a){
this.name = n;
this.age = 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 code The code is as follows:

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

Method 3

Copy code The code is as follows:

function Person(n,a){
this.name = n;
this.age = a;
if(this.constructor === arguments .callee){
alert('new call');
}else{
alert('function call');
}
}
var p = new Person(' jack',30); // --> new call
Person(); // --> function call

seems perfect, but when the function/class is used as There is a problem when calling the method of the own instance object

Copy the code The code is as follows:

function Person(n,a){
this.name = n;
this.age = a;
if(this.constructor === arguments.callee){
alert('new call' );
}else{
alert('function call');
}
}
var p = new Person('jack',30); // new object first
p.fn = Person; // Assign the function/class Person to the fn attribute of the own object p
p.fn(); // When calling this sentence, it prompts "This is a new call", which is obviously wrong

Is there a better way?