Effect of "new" in JavaScript

Question

I have written some code I found in a video, and it looks something like this:

var clientX = clientX || {} ; 
clientX.MyClass = function(initialValue){
  var var1 = initialValue;
  var publicMembers = {
    get_var1 : function(){
      return var1; 
    }
  };
  return publicMembers;
}



var result = new clientX.MyClass("val1");
alert(result.get_var1());

clientX.instance = new  clientX.MyClass("val2");
alert(clientX.instance.get_var1());


clientX.instance2= new clientX.MyClass("val3");
alert(clientX.instance2.get_var1());

The thing is, after deleting the "new" keyword when I use : var result = new clientX.MyClass("val1"); Nothing is changed, so why the author chose to use it? What's the effect?

possible duplicate of What is the 'new' keyword in JavaScript? — Henrik Andersson
– Henrik Andersson, Commented Jan 7, 2015 at 20:33

Quentin · Accepted Answer · 2015-01-07 20:33:49Z

5

The MyClass function makes no use of this and has an explicit return value, so the use of new has no practical effect whatsoever.

answered Jan 7, 2015 at 20:33

Quentin

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Comments

Liam Schauerman · Accepted Answer · 2015-01-07 20:38:49Z

the new keyword is used as a piece of pseudoclassical instantiation, wherein a constructor object has properties attached to the keyword "this" but no return value is ever written.

var Car = function(){

  this.color = 'blue';
  this.make = 'toyota';
  this.model = 'camry';

}

now, writing var x = new Car() will add the following lines to the interpretation:

var Car = function(){
  var this = {}; //added by new
  this.color = 'blue';
  this.make = 'toyota';
  this.model = 'camry';
  return this; //added by new
}

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