JavaScript's new operator

In a previous post we explored the class-ical programming paradigm in JavaScript
The constructor pattern is a fundamental aspect of the class-ical paradigm
A constructor is code using which objects can be created from a class using the 'new' keyword
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Under the hood, JavaScript uses it's prototypal mechanism to support this feature. In other posts I explore the prototypal form in depth. For now, lets try to understand how 'new' works:

Lets create a function Person to behave like a Java Class

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function Person(first, last) { this.first = first; this.last = last; } var s = new Person("Deepak", "Anand");

Here are the things that happened after the last line was executed:

1. new creates a new object, lets call it this
2. the (constructor) function Person is called like so: this.Person ("Deepak", "Anand")
3. this is returned

Using upper-case for function-names that are used as constructors is convention only, not a language construct.

Now, what if you want methods in your "class"
Easy enough....

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function Person(first, last) { this.first = first; this.last = last; this.getFullName = function() { return this.first + ' ' + this.last; }; this.getFullNameReversed = function() { return this.last + ', ' + this.first; }; }

This works, but is not very efficient. For every Person instance, 2 function objects are created.
The solution is to add methods to the function's prototype property like so:

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function Person(first, last) { this.first = first; this.last = last; } Person.prototype.getFullName = function() { return this.first + ' ' + this.last; }; Person.prototype.getFullNameReversed = function() { return this.last + ', ' + this.first; };

References:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new
https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript