example code for comment to blog post: http://evanprodromou.name/2013/02/08/on-using-this-exactly-once/

on-using-this-exactly-once-part-1.js

function Person(/* whatever args your gonna have*/) {
	this.onSave_   = this.onSave.bind( this );
	this.onSetAge_ = this.onSetAge.bind( this );
}

Person.prototype.save = function() {
	this.database.insert( this.properties, this.onSave_ );
};
Person.prototype.setAge = function( newAge ) {
	this.constructor.validate( "age", this, newAge, this.onSetAge_ );
};

Person.prototype.onSave = function( err, result ) {
	if ( err )
		throw err;
		
	this.properties = result;
};
Person.prototype.onSetAge = function( err, result ) {
	if ( err )
		throw err;
	
	this.age = result;
};

on-using-this-exactly-once-part-2.js

;!function( Super ) {
	function ExquisitePerson() {
		Super.apply( this, arguments );
	}
	
	ExquisitePerson.validate = Super.validate;
	
	ExquisitePerson.prototype = Object.create( Super.prototype );
	
	ExquisitePerson.prototype.setAge = function( newAge ) {
		newAge *= .67; // equisite type persons age much more slowly than normal sucker type persons
		Super.prototype.setAge.apply( this, arguments );
	};
	
	ExquisitePerson.prototype.onSave = function( err, result ) {
		Super.prototype.onSave.apply( this, arguments );
		// do something exquisite here to disriminate against normal sucker type persons in favour of equisite type persons
	};
}( Person );

@TryingToImprove I believe the ; at the beginning is a guard against other js files that can come before this file during concatenation. Basically if those other js files make use of automatic semicolon insertion, that might cause some problems. There was a lot of discussion about this when Twitter Bootstrap coders refused to use semicolons, and this caused problems for some people (especially those using Crockford's JSMin).

The ! is there since function () {}() is not valid. An alternative, and I think better version is (function () {})(). This is called an immediately invoked function expression (IIFE). See http://stackoverflow.com/questions/3755606/what-does-the-exclamation-mark-do-before-the-function for more info.

@TryingToImprove I find the best explanations to IIFE in http://benalman.com/news/2010/11/immediately-invoked-function-expression/