ES5 syntax, how JavaScript determines whether a function is new or () called

The ES5 syntax does not support class classes, but you can declare a class by clearing the function as follows:

function person (name) {

This.name=name;

}

var john=new person (' John ');

Console.log (john.name);//john

But this class can be called directly like function execution: person ()

The decision is not to be called by New or () so modify the above class:

function person (name) {

This.name=name;

if (this instanceof person) {

Alert (' New call ');
}else{
Alert (' function call ');
}

}

New person (' Xiaoqiang ')//=> new call

Person (' Xiaoqiang ')//=> function call

Also in the wording can be easily copied and pasted into any class inside the following:

Notation 1:

function person (name) {

This.name=name;

if (this instanceof Arguments.callee) {

Alert (' New call ');
}else{
Alert (' function call ');
}

}

New person (' Xiaoqiang ')//=> new call

Person (' Xiaoqiang ')//=> function call

Notation 2:

function person (name) {

This.name=name;

if (this.constructor = = = Arguments.callee) {

Alert (' New call ');
}else{
Alert (' function call ');
}

}

New person (' Xiaoqiang ')//=> new call

Person (' Xiaoqiang ')//=> function call

It looks like the top three types are perfect, but how to call you will blind you

var jack=new person (' Jack '); =>new Call

Jack.f=person

Jack.f (' Don't believe you try ')//=> new call

ES5 syntax, how JavaScript determines whether a function is new or () called