Java Reference
In-Depth Information
This uses the set() method of the property descriptor. The argument of this is the value
that's assigned to the property. In the example this value is simply returned, implying that
the value of the sillyString() property has been set to the string "Hello" . We can
check the value using the dot notation:
<< "Craaazy!"
This calls the get() method, which ignores the value returned by the set() method and
returns the string "Craaazy!" , regardless of the value that was assigned to the property.
These methods give you much more power in controlling the way property assignment
works; however, they should be used sparingly and with care, as changing the expected be-
havior of an assignment has the potential to cause a lot of confusion.
The get and set property descriptors are particularly useful for controlling the getting
and setting of properties in constructor functions. In the example that follows, the Dice()
constructor function has been rewritten so that sides is now a private variable. We can
then use the sides property to create a get function that will return a description of the
number of sides, rather than just the actual number and a set function that prohibits a non-
positive number of sides to be set:
var Dice = function() {
"use strict";
var sides = 6;
Object.defineProperty(this, 'sides', {
get: function() {
return "This dice has " + sides + " sides";
set: function(value) {
if(value > 0) {
sides = value;
return sides;
} else {
throw new Error("The number of sides must be
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