// From JavaScript: the definitive guide, 5th edition
// This function adds property accessor methods for a property with
// the specified name to the object o. The methods are named get<name>
// and set<name>. If a predicate function is supplied, the setter
// method uses it to test its argument for validity before storing it.
// If the predicate returns false, the setter method throws an exception.
//// The unusual thing about this function is that the property value
// that is manipulated by the getter and setter methods is not stored in
// the object o. Instead, the value is stored only in a local variable
// in this function. The getter and setter methods are also defined
// locally to this function and therefore have access to this local variable.
// Note that the value is private to the two accessor methods, and it cannot
// be set or modified except through the setter.
function makeProperty(o, name, predicate) {
var value; // This is the property value
// The setter method simply returns the value.
o["get" + name] = function() { return value; };
// The getter method stores the value or throws an exception if
// the predicate rejects the value.
o["set" + name] = function(v) {
if (predicate && !predicate(v))
throw "set" + name + ": invalid value " + v;
else
value = v;
};
}
// The following code demonstrates the makeProperty() method.
var o = {}; // Here is an empty object
// Add property accessor methods getName and setName()
// Ensure that only string values are allowed
makeProperty(o, "Name", function(x) { return typeof x == "string"; });
o.setName("Frank"); // Set the property value
print(o.getName()); // Get the property value
o.setName(0); // Try to set a value of the wrong type
