JavaScript - interesting trick, it is possible to create both class and function in one definition

In this article, we're going to have a look at how to create class that allows user to create object with or without new operator in JavaScript.

Problem overview:

function MyClass() { }

var object1 = MyClass();
var object2 = new MyClass();  // <----- how to make new operator optional?

Simple problem solutions are presented below:

1. Optional new operator for class object with strict mode example

In this case recept how to make new object for same class definition with and without new keyword with strict mode is described.

Note: these approach work for web broser and NodeJS JavaScript with strict mode.

1.1. this or new object example

When this is not defined new object is cteated and assigned to self variable - it means ClassFunction was called as function.

// ONLINE-RUNNER:browser;

'use strict'; // optional for NodeJS

var ClassFunction = function() {
    var self = this || { };
  	self.printText = function(text) {
        console.log(text);
    };
    return self;
};

var object1 = ClassFunction();
var object2 = new ClassFunction();

object1.printText('This text comes from function result object!');
object2.printText('This text comes from class instance object!');

1.2. Using instanceof operator example

Below example shows how to detect if new keyword were used to create ClassFunction.

// ONLINE-RUNNER:browser;

'use strict';

var ClassFunction = function() {
    var self = this;
  	if (self instanceof ClassFunction) {
    	self.printText = function(text) {
        	console.log(text);
    	};
    } else {
    	return new ClassFunction();
    }
};

var object1 = ClassFunction();
var object2 = new ClassFunction();

object1.printText('This text comes from function result object!');
object2.printText('This text comes from class instance object!');

2. Optional new operator for class object without strict mode example

In this case recept how to make new object for same class definition with and without new keyword without strict mode is described.

2.1. Dedicated runtime environment example

Note: this approach requires to adjust source code for web browser or node js - look on comment - to solve this problem check example 2.

// ONLINE-RUNNER:browser;

var ClassFunction = function() {
    var self = (this == window || this == null ? {} : this);  // for web browser
//  var self = (this == global || this == null ? {} : this);  // for nodejs
  	self.printText = function(text) {
        console.log(text);
    };
    return self;
};

var object1 = ClassFunction();
var object2 = new ClassFunction();

object1.printText('This text comes from function result object!');
object2.printText('This text comes from class instance object!');

2.2. Web browser or NodeJS auto detecting

This universal approach is useful to write code for web browser and node js both.

// ONLINE-RUNNER:browser;

function getRoot() {
    if (typeof window != 'undefined') {
      	return window;
    }
    if (typeof global != 'undefined') {
      	return global;
    }
  	throw new Error('Unsupported platform!');
}

var root = getRoot();

root.createScope = function(self) {
  	return (self == root ? { } : self);
};


// Example:

var ClassFunction = function() {
    var self = createScope(this);
  	self.printText = function(text) {
        console.log(text);
    };
    return self;
}

var object1 = ClassFunction();
var object2 = new ClassFunction();

object1.printText('This text comes from function result object!');
object2.printText('This text comes from class instance object!');