One of the things you learn early on when manipulating a DOM using Javascript is the following pattern:

var img = new Image();   // Create new Image object
img.onload = function(){
  // execute drawImage statements here
}
img.src = 'myImage.png'; // Set source path

As far as I know, in general when you set an object property there are no side effects. So what is the mechanism for triggering an image load? Is it just magic? Or can I use a similar mechanism to implement a class Foo that supports a parallel pattern?

var foo = new Foo();   // Create new object
foo.barchanged = function(){
  // execute something after side effect has completed
}
foo.bar = 'whatever'; // Assign something to 'bar' property

I'm vaguely aware of Javascript getters and setters. Is this how Image.src triggers a load?