javascript

Chapter 5: Reference Types
This function ’ s syntax may look complicated, but essentially it ’ s just a function inside of a function,
preceded by the return operator. The propertyName argument is accessible from the inner function
and is used with bracket notation to retrieve the value of the given property. Once the property values
are retrieved, a simple comparison can be done. This function can be used as in the following example:
var data = [{name: “Zachary”, age: 28}, {name: “Nicholas”, age: 29}];
data.sort(createComparisonFunction(“name”));
alert(data[0].name); //Nicholas
data.sort(createComparisonFunction(“age”));
alert(data[0].name); //Zachary
In this code, an array called data is created with two objects. Each object has a name property and an
age property. By default, the sort() method would call toString() on each object to determine the
sort order, which wouldn ’ t give logical results in this case. Calling createComparisonFunction
( “ name “ ) creates a comparison function that sorts based on the name property, which means the first
item will have the name “ Nicholas ” and an age of 29. When createComparisonFunction( “ age “ ) is
called, it creates a comparison function that sorts based on the age property, meaning the first item will
be the one with its name equal to “ Zachary ” and age equal to 28 .
Function Internals
Two special objects exist inside a function: arguments and this . The arguments object, as discussed in
Chapter 3 , is an arraylike object that contains all of the arguments that were passed into the function.
Though its primary use is to represent function arguments, the arguments object also has a property
named callee , which is a pointer to the function that owns the arguments object. Consider the
following classic factorial function:
function factorial(num){
if (num < = 1) {
return 1;
} else {
return num * factorial(num-1)
}
}
Factorial functions are typically defined to be recursive, as in this example, which works fine when the
name of the function is set and won ’ t be changed. However, the proper execution of this function is
tightly coupled with the function name “ factorial “ . It can be decoupled by using arguments
.callee as follows:
function factorial(num){
if (num < = 1) {
return 1;
} else {
return num * arguments.callee(num-1)
}
}
126